Gender Is No Object

A lot of media (especially science fiction and fantasy) features societies with no gender restrictions. Women fight alongside men, in the same combat roles, in command, and so on. Because it's a societal norm, no one considers this unusual. Hereditary monarchies can be ruled by women as well as men, despite a real-world historical restriction on women ruling the kingdom.

This is NOT the same as splitting the sexes up into segregated units. When this trope is used, mixed units are the norm, and by extension often a completely integrated society as well in which the only difference between the sexes, in a social sense, is that one can get pregnant and the other can impregnate. In an Science Fiction story where test-tube-and-incubator babies are common, even this is removed and if the soldier is encased in armor, you can't tell what gender he/she is, and it doesn't matter anyway.

Be careful: not every story about women serving in the military is an example of this trope. Stories where the majority of military units are male and occasionally you find a girl (Ender's Game, for example) do not apply. Nor do militaries where women are common, but are restricted to certain roles (especially if those are noncombat roles). Nor do stories where there are women in combat roles, but they are consistently portrayed as falling into the Damsel in Distress or Faux Action Girl trope.

This can be a Justified Trope, especially in futuristic settings where advances in technology have made physical differences like gender more or less irrelevant for soldiers. In medieval fantasy settings, authors may introduce some form of safe, reliable Fantasy Contraception, or the existence of inborn magic powers can be portrayed as making differences in size and strength less relevant, or there may be other social pressures encouraging gender equality (although all of these may or may not be convincing, depending on how well they're handled). If the setting is not Earth and/or the characters are not normal humans, they may just have less sexual dimorphism. On the other hand, there are also plenty of cases of lazy or thoughtless worldbuilding, as well as cases where the author simply felt they needed no justification beyond Rule of Cool.

There are a wide variety of possible reasons for this. Sometimes it's pure Author Appeal: the author thinks a mixed-sex military setting is simply more awesome than a segregated one, or wanted to write about heterosexual relationships within such a setting, or wanted to have a female protagonist in such a setting without having to worry about showing her struggling with prejudice. In role-playing games (video or tabletop), it may be done to make sure players are never penalized for wanting to play a character of their own gender. Sometimes it's an Author Tract (or, in the best case scenario, a case of Some Anvils Need to Be Dropped), with the author trying to make a point about how gender restrictions are good or bad.

For a related, video game-specific trope, see Purely Aesthetic Gender. Not to be confused with a person for whom gender is no object.

Anime and Manga

 * Fullmetal Alchemist Any and all of the women shown, especially the ones in the millitary, KICK ASS. We have Major General Olivier Mira Armstrong "The Wall of Briggs", Lt. Riza Hawkeye (who's pretty much the only one who can keep the Colonel under control), and Lt. Maria Ross (Not as Badass, but important nonetheless). And let's not even start on Izumi...
 * Actually far closer to the The Squadette than this trope, while there are a few female soldiers and alchemists the vast majority are still male.
 * Magical Girl Lyrical Nanoha The TSAB Armed Forces (and probably the Saint Church Knights) in the franchise make no gender distinctions whatsoever (although most notable characters are female, but that comes with the genre, not the setting), and there isn't even a single instance of Wouldn't Hit a Girl in the series. In-universe, this is justified by the TSAB being extremely short on hands, since powerful mages are very rare.
 * Pokémon Despite carrying the label of "training for girls" by the Fanon, in the anime, there are equal gender amounts of Coordinators as there are Trainers.
 * Examples of this are present in the gritty, gang orientated setting of Michiko to Hatchin were:
 * Hatchin is a proud, hard working (pretty much handyman) little girl who sticks to her morals
 * Mitchiko is a Good Bad Girl; a law breaking drifter focused on one objective - she gets into scraps with men who frankly don't care if she's a lady
 * Atsuko; Michiko's childhood friend, ventured down a polar opposite 'career' path - becoming a relentless law enforcer
 * Zeta Gundam. Captain Bright: "This is the military! Gender is irrelevant!" Although Kamille does note that women serving in the military in equal capacity is a relatively new development for the Universal Century.

Film

 * GI Jane The film's aesop is that militaries should be this way.

Literature
"Cordelia: The more physical jobs are skewed to the men, of course, but there doesn't seem to be this obsessive status-thing attached to it."
 * The Branion series, by Fiona Patton, set in a fantasy Europe where gender roles are unrestricted. The oldest noble heir inherits regardless of sex, and religious posts (in thinly disguised versions of Christianity) are also open to all.
 * The Circle of Magic series, by Tamora Pierce, although told mostly from the point-of-view of female characters, features more-or-less gender parity within the temple, the army, and society at large. Some cultures have more restrictive views of the roles of women, but the viewpoint characters visiting said cultures always point this out.
 * Pierce's Beka Cooper books, in the Tortall Universe, features this, but a religious movement called the Cult of the Gentle Mother is sweeping through and starting to influence things, much to the wrath of the protagonist. From later-set books we know that it does take over and become the norm for later protagonists to struggle against.
 * The Culture takes this trope Up to Eleven. Not only have they left gender roles far behind, part of their standard set of genetic enchantments is the ability to go through a fully functional sex change (over the course of several months) at will. The protagonist of The Culture is considered a bit odd because he's never even tried being female.
 * The Deed of Paksenarrion The mercenary troops.
 * Discworld dwarfs, initially. It turns out to be more complicated than that later on; biological sex seems to be genuinely inconsequential except for procreative purposes, but traditional dwarf culture has no concept of femininity and both sexes look like men, so they're basically a One-Gender Race of men that just happens to have two different kinds of genitals. Traditionally, anyways. Midway through the series (beginning with Feet of Clay), some more modern female dwarfs begin to admit to being female and adopt human-style feminine behaviour, which is controversial but increasingly popular.
 * Dragaera The culture of the titular empire is like this.
 * The Earths Children books by Jean M Auel . The Cro-Magnon.
 * The Forever War is similar to Starship Troopers but features a fully gender-integrated military... which before the end of the war is also fully homosexual as Earth society has moved on about a thousand years, literally.
 * The Gentleman Bastard sequence, there are female pirates, thieves, soldiers, sailors, and bouncers in about equal number to their male counterparts. This is never remarked on as being out of the ordinary. In fact, within their culture, rather than women being banned from sailing for fear of bringing bad luck, ships are required to have at least one woman on board, to avoid bringing the wrath of the sea god (though a female cat will do at a pinch).
 * Hammer's Slammers by David Drake. The Mercs.
 * In the Honor Harrington series, this is pretty much the default for the major interstellar polities. In the story, the reactions to integration by Grayson and Masada (both worlds being effectively religious patriarchies, with the latter treating women as nothing but property) often play a major role in the plot.
 * In Inheritance Cycle, female elves are just as good fighters as male elves.
 * The Left Hand of Darkness by Ursula Le Guin takes the basic idea so far it almost becomes disqualified as an example, as the human-descended people on the planet Gethen are all of both sexes (or neither); they take turns becoming "male" or "female" for reproduction. The human-as-we-know-it protagonist is really confused by this even after years of living there as an ambassador of sorts.
 * The Malazan Book of the Fallen Most of the cultures are largely this, especially the dominant Malazan Empire.
 * The Quarters series by Tanya Huff plays this trope totally straight. Interestingly, though, it also draws attention to the trope by referring to many minor or background characters by their occupation -- "two guards," "a secretary" -- a few lines before the gendered pronoun is used. The reader then realizes that the guard or secretary to which s/he had unthinkingly assigned the "conventional" gender is, in fact, just the opposite.
 * It is worth noting that in this series, sexual orientation is no object either; even royal weddings can be same-sex.
 * The main character of the Confederation of Valor series (same author) is a female Space Marine Gunnery Sergeant. More generally, the Confederate armed forces have more men than women, but this seems to be a simple case of men being more likely to sign up.
 * Redwall's later books do this. The first book had female combatants on the heroes' side, but no mention of female Mooks at all. Later books introduce better gender equality for both sides.
 * Seafort Saga by David Feintuch, cadets and middies are treated the same regardless of their gender. This extends to mixed sleeping quarters and bathrooms, with it being said that your mates are like family (so having sex with them is a bad idea).
 * The Star Wars Expanded Universe. The films feature largely male-dominated militaries - some of the Jedi are women, as is Princess Leia, but most women aren't close to combat at all in either trilogy. The Expanded Universe changes this. Admittedly there aren't a lot of non-clone humans in Clone Wars works period, but works set around and after the original trilogy integrate the ranks of the Rebellion / New Republic, and to a lesser extent the Empire. Gender really isn't brought up in the Rebellion / New Republic, but there are women in every position - admirals and generals down to pilots and commandos. In the Empire, women fall into the NonhuMan category, which includes women, cyborgs, nonhumans, and droids, but some of them still claw their way up the ranks. There are more female Imperials than there are nonhuman Imperials.
 * Vorkosigan Saga by Lois McMaster Bujold. Everybody but the Barrayarans seem to have mixed military. The Betans especially seem to have no social differentiation between genders (and hermaphrodites) in their space service or society. Being a neutral world, they tend to sit out on most wars and don't really keep an actual military, but their science/astrocartographers/explorers have military training and fulfill that need as necessary. The Barrayarans' inability to process the idea of women soldiers works against them in the first book, as they not only hesitate to shoot the female protagonist (bad idea), they consistently underestimate her.


 * Which, in a culture as technologically advanced and reliant as Beta Colony, makes a lot of sense.
 * In The Keys to The Kingdom, the House seems to work this way.
 * The titular city-state in the Liavek anthologies is very egalitarian gender-wise, including the military.
 * According to Ciaphas Cain (HERO OF THE IMPERIUM), mixed-gender regiments are rare in the guard, and most are male or female only. It's even implied by the (female) narrator they get female commissars, because they certainly wouldn't take orders from a mere man.
 * District Thirteen in Mockingjay seems to be this, particularly when it comes to their military. For that matter, the actual Hunger Games are deliberately set up with an equal number of boys and girls, and the audience makes bets on the contestants according to their skill and temperament, not their gender.
 * Warrior Cats: the Clan society has almost perfect gender equality, with equal numbers of female leaders and warriors throughout. The only real difference in how they're treated is when a female warrior becomes pregnant: she spends a few months in the nursery to have her kittens.

Live Action TV

 * Battlestar Galactica Reimagined The rebooted series eats, sleeps, and breathes this trope. There are women in every major role of life, from "knuckledraggers" like Cally all the way up to President of the Colonies Laura Roslin. Men, likewise, often fill traditionally "female" roles like religious leader, diplomat, and secretary. All living quarters for the rank-and-file soldiers are unisex as well, including bathrooms.
 * Star Trek Starfleet is supposed to be purely integrated; with gender no hindrance to attaining any position. The shows themselves often didn't quite meet this lofty principle.
 * Star Trek the Original Series suffered from Fair for Its Day, featuring female crewmembers who had as much authority as the writers thought they could get away giving them.
 * "Number One", Majel Barrett's character in the original Star Trek the Original Series pilot, was the ship's first Executive Officer before being replaced. Gene Roddenberry claimed this was because studio executives pressured Roddenberry to tone this trope down because they insisted that Viewers are Morons and couldn't handle women in any role other than secretaries and love interests. Other people involved at the time insist it's because the studio considered it unprofessional for him to cast his mistress in the role; they had no problem with the character, only with the choice of actress.
 * As did Majel Barrett. She said that when they tested the Pilot that women viewers did not like a woman as the Number One. One reaction was, "Who does she think she is?"
 * The villain in the episode "Turnabout Intruder" says at one point that women cannot be starship captains. She has since been retconned into an Unreliable Narrator. Reasonable, given that Dr. Janice Lester was barking mad (let's face it, switching bodies with Kirk with the intention of living the rest of your life as him is not the act of a sane woman).
 * Let's not forget that officers comprise a small portion of a ship's complement, usually a quarter at most. So, simply by being an officer, as many female characters were, a woman had authority over at least half the ship.
 * Star Trek the Next Generation slightly improved this with female security chief Tasha Yar. Of course, this meant she was prone to The Worf Effect and thus generally came off as incompetent. They eventually dropped a bridge on her at the request of Denise Crosby, the actress who played Yar, who had grown disillusioned with her role because of the "Uhura-like" status of her part. The only other lead female roles were in the caregiver roles of Doctor and Counselor.
 * Both Crusher and Troi eventually subverted this. Beverly was resident Combat Medic and the night-shift captain, and Deanna was also shown taking her officer's test and commanding the ship.
 * Star Trek Deep Space Nine featured Major Kira as the station's second in command, but she wasn't actually a member of Starfleet. Lieutenant Dax, on the other hand, was the station's operations operator and second officer (meaning, she supposedly was in command when Sisko and Kira weren't around).
 * Of course, Lt. Dax is also a Trill, whose relationship with this trope is... rather complicated.
 * Star Trek Voyager It wasn't until here that one of the Trek series actually reached this lofty principle with a leading female character as Captain (although female captains and admirals did appear in minor, one-shot background roles from The Next Generation onward. There was also the first female Chief Engineer, and a woman in the role of a prominent scientist (yes, Seven did other things than wear a catsuit).
 * Star Trek Enterprise has T'Pol, resident Ms. Fanservice and Number One at the same time. (Archer tends to ignore her, but that's more because he has a chip on his shoulder re: Vulcans, and ignoring your Vulcan first officer is a time-honored Star Trek tradition.) There are also a number of women in the security division and MACOs, plus the captain of the Columbia, Starfleet's second Enterprise-class starship.
 * Peacekeepers practice a lot of Fantastic Racism and are usually played as kinda evil, but sexist they are not. Aeryn was a pilot, Grayza a Commandant, Xhalax a Senior Officer, etc. and whenever large groups are shown there are always plenty of females in the ranks. Aeryn does mention "female units" when explaining their Fantasy Contraception, but there are far more examples of mixed units throughout the series.

Tabletop Games

 * Eclipse Phase most obviously follows this trope and goes beyond it. In the Transhuman future where bodies are just a shell that can be swapped easily (although expensively) all bodies come with built in immunity to sexually transmitted infection and can chose if they become pregnant or not, any and all conventional ideas of gender have pretty much fallen by the wayside. In the game you have a separate gender for your body and mind and its up to the players how they deal with that. Unless you do very extensive research there is no real way to KNOW what gender a person is if they want to act male or female. Since not all people are human, or indeed humanoid, the issues presented in the game much more strongly run along species/artificial life prejudice than gender.
 * Slightly subverted in the case of the 'Fury' morph. This is a combat body that is built to be strong and tough and kick some serious butt, but the designers made them all women to give them a better inclination towards teamwork and less naked aggression.
 * RPGs in general. There's no restriction on character gender in most of them, with Dungeons & Dragons the most obvious.
 * Though we must point out that 1st edition D&D had a "fighting man" class, and there is an apocryphal story about Gary Gygax killing a character without a save in the first round of combat because "girls can't fight".
 * Not apocryphal, however, is Gygax's essay in the PHB talking about why players shouldn't be allowed to play monsters or female characters, because it would be too hard to play something they're not. Because, I mean, obviously, no girls play D&D, and their mindset is completely alien...
 * And there was a quickly excised rule that female characters automatically had a penalty for their strength (in turn getting a slight bonus to their Charisma). See Game Favored Gender.
 * What the game did have, all through 1st Edition, was an upper limit on female strength - it affected only those females who played fighters, rolled an 18 for strength, followed by 51% or higher on the "exceptional strength" bonus. Anyone of either sex who wasn't a fighter didn't roll the bonus percentage even if they had an 18 strength, nor (obviously) did anyone who didn't have an 18 strength in the first place; and the various belts and gloves that conferred fantastic strength worked just fine regardless of the gender of the wearer. Eventually TSR caved and this rule went the way of all flesh.
 * For female humans, that was the extent of the issue. Female demihumans' Strength-ceilings often kicked in a full point before their male counterparts', placing them at a serious disadvantage in combat classes. This, for races in which biological gender differences were otherwise less overt than humans'.
 * Dragon Magazine's letter column had one particular GM explaining his "balanced" houserule for his games, where female characters received a -2 strength penalty in return for the advantage of being capable of bearing children. The replies were... agitated, to say the least.
 * An interesting in-universe case: although there are no technical restrictions for the player characters, Drow society is pretty much 50% Evil Matriarch, 50% Always Chaotic Evil everyone else. Many players of male Drow (who aren't just trying to be Drizzt version 2 play themselves as having come out of the Underdark so they can have better goals in life than being the "lucky" consort of a powerful enough woman that gets to be a walking sperm bank for longer than a few mating sessions before she tires of him.
 * 1st Edition rules blatantly enforced drow gender differences, giving their sexes different ability ranges and class advancement limits.
 * Even Role Playing Games that are semi-historical tend to skirt round the issue. Games like Deadlands: Reloaded and Spirit of the Century have brief side notes concerning problems with playing in the time periods with regards to gender and race, but for the most part they brush it aside and assume it is largely irrelevant.
 * Somewhat justified in that in these, and most other, RPGs the player characters are exceptional people, so they can overcome the usual drawbacks of gender (and/or race) of their times, as exceptional people throughout history have.
 * Legend of the Five Rings in its first edition had a brief essay by John Wick explaining that there was no possible way to justify female player characters in the setting ... but, as that wasn't fun players and the GM should ignore it and allow them anyway.
 * Battle Tech As backward as the Feudal Future may seem at times, gender equality is pretty much the universe-wide default. Even in the (explicitly matriarchal) Magistracy of Canopus. Though the Draconis Combine does seem to have fewer military women in general compared to the others (and there are certainly issues with the Coordinator being a woman, which only happened once in Combine history), it still has quite a few. Then again, the DC is probably the least pragmatic of the 5 great houses when it comes to fighting.
 * The Clans play this even straighter, especially in the warrior caste. You will see men and women at every level of their military hierarchy and no one bats an eye at a female Galaxy Commander or Khan. Considering that a family unit and marriage do not exist among warriors and all reproduction is handled artificially (often after the parents are long dead) its safe to safe that the Clans have no social distinction between genders.
 * Traveller This varies from culture to culture. The ruling class of the Third Imperium is like this however.
 * It varies from service to service in the Imperium of Man, but most governmental, religious, and (in some cases) noble positions are gender-blind, as are the Inquisition, the Adepta Astra Telepathica, Rogue Traders, and the Adeptus Mechanicus. Some are segregated, though - the Space Marines are all men, evidently due to the genetic engineering required to make them, while the Sisters of Battle are all women because the Ecclesiarchy is banned from maintaining "men under arms". In the Imperial Guard, most regiments are single-gender, and men outnumber women roughly 9-to-1, but female officers and regiments are just as honored, and mixed-gender regiments are not unheard of. They are distinctly outnumbered in the higher ranks, though; one Mauve Shirt from the Ciaphas Cain series eventually reaches the exalted rank of Lady General, but is among the only ones in recent history to have done so.
 * The Imperium is also completely uncaring about who fights for them as long as they can hold a gun, its a commonly mentioned background element that when the Imperium is desperate enough or when they just need a few more warm bodies to pad out the ranks that they will mass-conscript children to fight for them so not only is gender no object age isn't either.
 * Paranoia makes a point that there is no practical difference between the genders. Between the fact that new clones are decanted, not born, and everyone is on pretty powerful hormone suppressants that keep emotion, sexual dimorphism, and most especially sexual impulses way down (the latter being removed entirely) this is extremely accurate. The only reason the game even has sexes at all (rather than assuming Alpha Complex produced straight up sexless clones) is to ensure that there's an added bit of humor when someone works out how to suppress the hormone suppressants.

Video Games

 * Computer role-playing games. This trope is true in many of them simply because female gamers play these games too. Usually, this trope is handwaved and never commented upon.
 * In very old PC Role Playing Games, however, it was common for there to be gender-based stat adjustments, usually with male characters getting a bonus to strength and female characters getting a compensating bonus to charisma, dexterity or intelligence. This, of course, had its own problems, which is why it's rarely seen anymore.
 * Age of Empires III had female characters who fully acted as combatants, which was never mentioned by anyone in-game.
 * The Elder Scrolls: Organized militaries like city guards and the Imperial Legion seem to have decidedly more men than women. More specifically, nameless guards and legionnaires are all men, but named ones can be either. Other organizations, as well as wilderness mooks, seem to be split about 60/40 between men and women. It seems that in this universe, there's nothing stopping women from signing up, but they just don't join up as often.
 * The Fallout universe has a fairly equal amount of female and male bandits, raiders, quest-givers and such. Justified in post-apocalyptic settings, really, since it would be stupid for society to waste any able pair of hands.
 * Until Fallout New Vegas introduced Caesar's Legion.
 * Your mileage may vary on the justification; one could argue that a decimated population would want to protect fertile women at all costs.
 * Final Fantasy VIII Male and female students and SeeDs at the Gardens train and fight together.
 * Fire Emblem mixes the genders readily, both in the army as a whole and within the different classes. Only a handful of classes are single-gender, including the all-women Pegasus Knight class.
 * Gears of War: The first two games and the novelizations subvert this. Only men do the fighting. All fertile women are used for reproductive purposes, while non-fertile women serve in support roles. The third game, however, plays this straight. The women fight alongside the men. This is because humanity is down to its last throes and needs every available body to fight.
 * Before Emergence Day active female Gears were not unheard of and were at least as common as female soldiers are today, some examples introduced in the Aspho Fields novel being Bernadette Mataki and Helena Stroud, Stroud being the commander of her own company and the mother of Anya from the games. Gender equality and civil rights took a nosedive after most of humanity was killed after E-Day and men became more expendable than women.
 * The Mass Effect universe seems to be gender blind when it comes to humans, for the most part. Possibly quarians as well, considering the only quarian military groups we ever see are lead by Tali and the Admiralty board splits 60/40. Other alien races don't show their females at all (the asari, being a One-Gender Race, don't count), but Garrus' war stories show that the turians are integrated too. Restrooms are still segregated, though, as EDI will remind you if you stumble into the wrong room. Maybe a Justified Trope with genetic enhancements being standard for soldiers of humanity.
 * Salarians do not follow this rule though, since their species breeds too few females to throw them into combat.
 * Tali and Ashley discuss this in the first game. Ashley mentions how long it took human women to prove they could handle shotguns, with Tali replying that the Flotilla can't afford the "luxury of sexism".
 * In Lair of the Shadow Broker one of the files states that infertile krogan females at least have garrison roles on their homeworld. All krogan are taught how to fight from childhood, it's a question of who they can afford to risk.
 * Interestingly enough, the first game plays with this trope a bit in terms of your options of NPC allies: classes that specialize in one form of warfare (Soldier, Adept, Engineer) are given to female characters (Ashley, Liara, and Tali, respectively). On the other hand, hybrid classes (Vanguard, Sentinel and Infiltrator) are provided by males (Kaidan, Wrex and Garrus). However, the Player Character, Shepard, can choose to follow this trend or avert it, based on their gender and class selection.
 * Dragon Age is a bit odd on this trope. There are plenty of female warrior NPCs, including among the soldiers, but it is noted that Grey Wardens are rarely female. And the evil shambling Darkspawn that we see on the surface attacking people are all male. These two facts are not completely unrelated.
 * World of Warcraft players abide by this trope, but the societies they're theoretically members of aren't necessarily so accepting. Most notably night elf warriors are female and druids are male.
 * The night elves are one of the few notable exceptions. For the vast majority of WoW's cultures this trope is played completely straight.
 * It's mentioned that, due to the casualties suffered during the war against the Legion in Warcraft III, the night elves have dropped their traditional gender requirements. (Also, they were only requirements for joining the Sentinels or formal druidic training, respectively - there's no rule that says a night elven man couldn't be a badass swordsman on his own.)

Web Comics

 * Order of the Stick is a good example; even in areas inspired by patriarchal societies (like Azure City) there are plenty of female warrior characters.
 * For elves, gender is literally no object
 * In the Schlock Mercenary universe, women can be found at all levels, from lowly grunts up to admirals commanding fleets and all over the civilian sphere, and aside from a few sexist comments here and there no particular note is taken of it.

Web Original

 * Ilivais X has the total characters of either gender exactly the same, in a setting where the only named characters are Super Prototype pilots or high-ranking military commanders. For the most part, the implication of prejudice for ANY group is highly frowned upon.

Western Animation

 * Antz does this with, well, ants, both in worker and soldier roles. It's one step better than the Insect Gender Bender, at least.
 * Avatar: The Last Airbender The Fire Nation's armies have men and women fight alongside each other, and even their prisons are unisex. Despite being the primary antagonists, they are unique in this respect. The Earth Kingdom army has few if any women (nothing is specifically stated, but none of the shots of their armies seem to involve women fighting). And the Northern Water Tribe explicitly forbids women from fighting, much to Katara's annoyance.
 * Though this could go rather far in explaining why the Fire Nation has been successful in their war. While healing is certainly a vital military role (which is what female waterbenders are relegated to in the NWT), not every female waterbender has healing powers. Those that don't are forbidden from being useful in a fight at all. Maybe the Fire Nation is winning because they are better able to use more of its population in a direct combat capacity due to simple pragmatism.

Real Life

 * Several European monarchies (IIRC, Sweden and Belgium) now allow the firstborn to inherit regardless of gender, and others are considering the change.
 * Japan seriously considered the change when the Crown Prince's daughter appeared likely to be his only child. Then his brother had a son, and the discussion ended.
 * England removed any limitations on gender when it came to their monarchy back with Queen Mary I (daughter of Henry VIII and older sister of Elizabeth I). It should be noted, however, that Mary only became Queen because her younger brother Edward (who had already reigned as King Edward VI) died with no heirs and she was next in line for the throne.
 * Likewise, Queen Elizabeth I only became queen because there was no closer male heir after her sister Mary died without having had any children. If Mary had kids, Elizabeth would have never reached the throne.
 * Actually the UK (and by extension the other Commonwealth nations that are still constitutional monarchies) still practise male primogeniture. What this means is that Prince Andrew and Prince Edward (and their children) are in front of Princess Anne and her children in the line of succession despite the fact she is the older than them. There is talk about changing this to straight primogeniture (order of birth without regard to gender) while it would leave the top spots in the succession order (Charles, William and Harry in that order) unchanged.
 * Changing the UK succession would require agreement from the entire commonwealth making it rather unlikely.
 * As long as the Commonwealth Realms decide to retain a united Monarchy, this is true. It's generally considered a good idea for the Realms to maintain the same monarch, but with all the main countries now fully independent, they could theoretically decide to change the succession rules according to their own values, meaning that the lines of succession would eventually split. But as stated above, that's currently very unlikely.
 * Too late, they already did.
 * The Dutch monarchs have been female for the past century (the next is scheduled to be male, although he has had 3 daughters so far, so the one after him will be female) with straight primogeniture. The only distinction can be found in the monarch's spouse: A King's wife gets the title of Queen, but a Queen's husband is not called King, but Prince-companion. Possibly, people were worried that King sounded more important than Queen, and didn't want others to think that the guy that married into the royal family was the big shot.
 * Also directly related to why the Luxembourgish monarchy is not following this trope. When a woman inherited the Dutch throne they basically dug up an old law that says only men can inherit theirs and thus won their independence. It's kind of hard to get rid of the tradition that made you independent. (Also there are no women currently in the position where they would inherit the position if it were possible, so there's no need to change it anyway.)
 * This is very similar to the role of the "Prince Consort" of the Commonwealth realms (Albert for Victoria, and Philip for Queen Elizabeth), which operates on the same principle: He married into royalty and has all the same perks, but he still must walk "one step behind" his Queen. The idea is basically the spear counterpart to the "Queen Consort" (a Queen who married into the family rather than a "Queen Regnant", which is a ruling Queen).
 * Modern-day monarchies tend to follow one of three patterns: gender is ignored (this trope, in other words), females can inherit, but males take preference (exactly how much preference is given varies, so this pattern incorporates a lot of variation), and females can't inherit.
 * Most modern military forces around the world allow women to serve in most roles. Generally, however, women are restricted from serving in front-line infantry or armored units, or special forces like the Navy SEALs. Most will claim it's out of a sense of fairness, and it may well be, but in a lot of cases it's initially motivated by a shortage of recruits.
 * Related to the front line issue, outright said in a movie (might even be Truth in Television) that it's bad for media relations if bodies of American young women get hauled off the battlefield.
 * In the US Navy there is a considerable roadblock in having facilities on ships and particularly submarines, since nobody yet thinks it a good idea to put generally young adults of opposite genders in the same small spaces while sharing restrooms and showers. Consequently female officers (who have much more private accommodations) can serve in more locations then enlisted female.
 * Canada's military is fully integrated and has been since 2001 when the last holdout (submarine service, for the entirely practical reason they didn't have submarines equipped for female crew members until then) had its prohibition against women serving aboard lifted.
 * The Soviet Union made much to do about the number of women in their Air Force. The first two women in space and the only two female flying aces were Soviets. They also had tankers, snipers and a good many partisans.
 * During The Great Patriotic War, yes. After the war as in Western countries there was strong pressure for women to return to their traditional roles as child-rearers.
 * Israel has one of the more gender balanced armies in the world. It's also one of the few where women are subject to conscription like the men, though they are more likely than men to get an exemption, and have to serve a minimum of two years instead of the men's three. They are placed in combat units only if they volunteer to do so, though it should be noted that most combat units are male exclusive due to potential problems with a unit's social dynamic (for example, tests have shown that male combatants tend to lose their better judgment when a female comrade is injured much more readily then if a male comrade is wounded). Though female pilots are still allowed and are relatively common.
 * While not all branches are fully integrated, the United States Coast Guard allows women to serve in all roles, and has females at all ranks, including several rear admirals.
 * Rear Admiral Grace Hopper, promoted 1983 to Commodore, a rank later renamed Rear Admiral.
 * There's a theory that ancient Neanderthal society might have been like this, with women and children joining men out in the hunt. This may have contributed to their decline at the hands of modern homo sapiens, whose women gathered instead of hunted (thus ensuring other, non-risky sources of food and a safer environment for their women and children. More healthy women and children equals a higher population.)