Shocking Defeat Legacy

In fiction (and in Real Life) during a great war there's a certain strategic loss that is very significant to the point of being demoralizing, shocking, and Iconic in universe. One faction might be fighting a intergalactic war with Scary Dogmatic Aliens, But there's one place in the galaxy that has no chance in hell of falling at the hands of the enemy. Perhaps it's a planet that's fortified by surrounding Kill Sat, a squadron of Sun Crushers and an armada of Titan-class motherships, guarded by battalions of Voltrons and other Combining Mecha, SDF fleets and Valkyries.

But in the end, said planet falls, sending a chilling wave down the spines of The Federation. Sometimes it could be a turning point in the war, but not always. A faction can suffer these defeats and not necessarily be defeated. But it's still a crippling loss that'll at least slow them down significantly. Sometimes these defeats are due to surprise attacks. Could end up as a Pyrrhic Victory for the attackers. Sometimes it's described as a Noodle Incident in some stories. This is usually The Worf Effect, but for battles/wars (or even sports) instead of individuals. Usually to show how high the stakes is.

Usually overlaps with Hopeless War, Remember the Alamo!, and Last Stand.

For the victors it could overlap with Pyrrhic Victory, and Was It Really Worth It?.

Anime and Manga

 * End of Code Geass season one when the Black Rebellion fails spectacularly in the throws of what almost looked like their Finest Hour. History Repeats in season two when the Black Knights are AGAIN defeated, this time by Lelouch, amplified by the fact that it means he now rules the world with an iron fist. Justified.

Film

 * The Rebel Alliance from Star Wars blowing up not only the first Death Star, but the second one as well.

Literature
"Han Solo: The end of the world. Who’d’ve thought we’d live to see it?"
 * The Battle Of Yonkers. They threw everything but the god damn kitchen sink at the enemy and still lost.
 * Though that was actually a detriment in the end, as all their gear and defenses and tactics were based on fighting an enemy that obeyed no human nor life norms (no pain, no fear, no stopping...)
 * The Fall of Coruscant to the Yuzzhan Vong in the New Jedi Order series. Under the incredulous eyes of many of the surviving characters, the lights of The City That Never Sleeps go out for the first time in several thousand years.

Live-Action TV

 * The Battle of Wolf 359 from Star Trek: The Next Generation.
 * The loss of Betazed in the Deep Space Nine series to the Dominion, and the destruction of Vulcan in the 2009 film too.
 * Also from Deep Space Nine, the Breen attack on San Francisco. Not as damaging as some of the others on this list, but shocking in that they were able to stab at the heart of The Federation.
 * The Battle of Serenity Valley in Firefly, which was apparently the battle that lost the war for the Independents and sent Malcolm Reynolds over the Despair Event Horizon.
 * In Doctor Who, much of the Last Great Time War between the Time Lords and the Daleks has only been explained through dialogue by the Doctor himself. However, we do have a definite shocking defeat that was said on the show: the Fall of the Cruciform, which was so shocking that it made the Master himself flee to the end of the universe.

MMORPGs

 * In World of Warcraft there are numerous examples of this, as well as a couple of subversions, but given the name of the game, that's hardly surprising. There is the War of the Ancients which led to the destruction of the Kaldorei kingdom and the world splitting apart. Then the Orcs almost complete annihilation of the Draenei on Draenor. After which, said orcs go on to invade the world of Azeroth and sack the human city of Stormwind. Later, they go on to enslave the Red Dragon Flight, with which, they almost reduce Quel'Thalas to burning ash. Later, Prince/Death Knight Arthas ends up killing every man, woman, and child in Stratholme. After that, he kills his father, several paladins, including another father figure, Uther, then sacks Quel'Thalas and Silvermoon City to use the Sunwell, which he then blows up. Oh yeah, at the end of that campaign, Archimonde comes around to completely demolish Dalaran. The Kaldorei lose their beloved demigod, Cenarius, in a battle with Grom Hellscream. Finally, the Kaldorei give up their immortality by blowing up the World Tree to kill Archimonde. Did I mention there were a lot of examples in this?

Video Games

 * The Fall Of Reach in the Halo universe. Which is the equivalent of America's CENTCOM, Norfolk Naval Shipyard, Fort Bragg, and Norad being taken out all at once.
 * The Covenant get one of their own by losing a whole armada of about 500 hundred ships thanks to Badass Admiral Cole.
 * By the year of 2552, The Covenant lost the Battle of Installation 04, which took a heavy toll on the Covenant. Later, after Prophet of Regret's death, The Covenant's capital city High Charity was conquered by the Flood. Since it the Covenant begun to become the losing side of the war.
 * In addition to the 500 ships The Covenant lost, they also lost 90% of The Fleet Of Particular Justice trying to destroy Reach. And what was left was utterly annihilated by the destruction of the aforementioned Installation 04. The prophets was so shocked and annoyed they gave Thel 'Vadamee (the fleet's Supreme Commander) a Promotion Demotion.
 * Deus Ex: the (French!) terrorist group blows up the Statue of Liberty!
 * Mass Effect has Shanxi, a human colony that was blockaded and sieged by the Turians during the First Contact War until it was forced to surrender. The DLC Bring Down the Sky features a devastating Colony Drop that heralds the return of the Batarians into galactic politics.
 * EVE Online has the battle of Vak-Atioth, a Curb Stomp Battle between the Jove and Amarr Empires, which sent the latter reeling into Vestigial Empire status. Later on, the Amarr reversed their fortune in the Battle of Mekhios, where they wiped out an entire Minmatar fleet and send the remnants of their forces packing.
 * Dragon Age has the Battle of Ostagar, in which the Player Character participates.

Western Animation

 * Avatar: The Last Airbender had Iroh's siege.
 * Not the best example, since the siege failed but didn't even slow the Fire Nation's progress. More appropriate examples would be the conquest of Omashu and Azula's coup in Ba Sing Se during the second season: the latter was particularly significant as Ba Sing Se was the last free city in the Earth Kingdom.
 * However, considering the effect it had on the line of succession in Fire Nation's monarchy, it was an important defeat nonetheless. The city of Ba Sing Se was sieged relentless off and on for a hundred years, but Iroh's siege is the only notable attempt to capture Ba Sing Se due to it being a turning point in the history of the Fire Nation, and as a result, the 100 Year War. Iroh's loss in favor gave Ozai an opportunity to make a claim on the throne, which was successful, and as a result of Ozai's leadership, the Fire Nation came dangerously close to winning once and for all. Shocking Defeat Legacy is not a killing blow or major surprise attack, but instead a defeat that no one saw coming and one that has major consequences. Nobody imagined Iroh's son would be killed, nor that as a result Iroh would retreat. If it were any other soldier, Iroh would probably have pressed the attack and won. Or, at least, that's what everyone was expecting to happen. He might still have lost, but that's irrelevant. It's the perception of defeat at the hour of victory or safety that defines this trope.
 * Iroh was a much better leader than Card-Carrying Villain Ozai, and if he hadn't retired, he would've found a way to crack Ba Sing Se open anyway, either with his original siege or later (he later managed it with a much smaller army, and against an army of comet-empowered Firebenders no less). Demoralizing Iroh and pushing him away from the war and the conquering mindset was the all-important coup which led to the Fire Nation's eventual defeat. Moreover, a hypothetical Fire Lord Iroh would have encouraged massive numbers of Les Collaborateurs due to his competence, winning personality and kindness, ensuring Fire Nation dominion over the Avatar world during his lifetime at least. Instead, Ozai succeeded Azulon, but he only really cared for himself and increasing his personal power, using and abusing even his favoured daugher and his country as a whole as tools to this end and running both ragged in the process; further, with his Complete Monster antics, he put all his enemies into a very motivating "do or die" situation, as well as adding his own son and brother, considerable powers in the world especially the latter, to their ranks. Any fight against Fire Lord Iroh would have been half-hearted at best, by comparison. TL, DR: It was this trope because it replaced Iroh's solid leadership with Ozai and his Villain Ball, a major strategic defeat for the Fire Nation.
 * Another example was the Day of Black Sun.
 * The loss of the Homeworlds for the Terrans in Exo Squad, although the late in the second season was an even more devastating blow to the Neosapiens. Phaeton built most of his anti-Terran propaganda upon it afterwards.

Real Life
"Winston Churchill:"I put the telephone down. I was thankful to be alone. In all the war I never received a more direct shock.""
 * Waterloo - So famous it's practically a synonym for defeat.
 * Although as with many battles, what gave Waterloo such a "knock-out blow" mystique that one tends to forget that fighting continued for quite a while after was not the battle itself but the subsequent pursuit. Thus in 1815, unlike 1812/13 and 1813/14, Napoleon's army was not given time to regroup and replenish.
 * Another example would be the Battle of the Berezina, which marked the end of Napoleon Bonaparte's squalid retreat from Russia. It was so bad, "une Berezina" became a synonym for catastrophe in France for a while afterwards.
 * Subverted with the Battle of Bailen - the Spanish destroyed three French divisions. Unfortunately, it was so shocking...that Napoleon turned up to sort the mess out in person, and promptly sent Spain into retreat.
 * The surprise attack on Pearl Harbour might count as one of these for the U.S.
 * Subverted, however, in that Pearl Harbor was for more catastrophic for Japan than the U.S. A tactical defeat for the U.S., but it added to what was already a hopeless war with China.
 * The Battle of Midway became this for the Japanese, as their loss in the battle effectively halted their expansion and put them fully on the defensive for the first time. US Naval Supremacy was only a matter of time, however; the Empire couldn't stay lucky forever in the face of the Allies' overwhelming economic superiority.
 * Another real life example would be the Battle of Hastings, as England would've ended up an entirely different country without it. Yet another real life example (and an often fictionalised one) would be the Battle of Chi Bi in the Romance of the Three Kingdoms, as it's widely believed that if the aggressors hadn't been defeated, the Three Kingdoms period might have ended then and there, which would have had a drastic impact on China's history.
 * Another example, although lesser known to Westerners, but with nearly as much impact on China's history is the Battle of Fei River. Had Jin lost, the Han Chinese could have lost control of China, however, Xie An (who was famous as a great administrator and had little military experience) decided he wasn't going to let Former Qin run wild and beat back a far more experienced army well over twice the size of his own. It was the single largest catalyst in the fall of Former Qin and just ten years later practically ceased to exist.
 * Hastings is a perfectly justified example, in that the King of England got an arrow to the head and his troops kept falling for fake retreats. Since few people really cared who was king at the time, William the Bastard Conqueror pretty much won by default.
 * Britain's 1940 retreat from Dunkirk marked a turning point in World War II, but is remembered in Britain more for the heroic rescue of stranded troops than as a defeat.
 * The "Fall of France" fits the trope name better. Dunkirk is more of snatching victory from the jaws of defeat (although Churchill was quick to point out that you don't win wars with retreats and that while it was great to save the troops, the Fall of France was still a major defeat for the Allies).
 * Also, they had to leave most of their heavy arms and equipment behind, so it would take a while before they were in a condition to face the Wehrmacht in the field again.
 * Which actually had a positive side in that it was New Improved equipment.
 * For the European colonial powers in general, and the UK in particular, the Fall of Singapore. It had been boasted that Singapore was the best-defended city in the world, the armour-piercing shells of her heavy gun emplacements capable of punching through any ship the Japanese had to offer. However, Singapore was besieged from the landward side, and their anti-battleship defenses were wholly ineffective at targeting infantry. Percival had 100,000 troops on paper, but they were in no shape to continue fighting. Realising that their situation was hopeless, he surrendered. Only to find that the Japanese only numbered some 30,000 and their supply situation had been even worse.
 * Churchill himself felt the fall of Singapore to the Japanese in 1941 was the greatest defeat in British history.


 * Vietnam was the greatest military quagmire in United States history.
 * Within the war itself, the Tet Offensive can be considered this. The vietcong attacked many cities simultaneously, notably claiming the US Embassy in Saigon. This was a major hit to the vision of American strength and hit their morale deeply. In reality, the vietcong suffered heavier losses than the American troops, but in terms of perception, this drastically swayed the war in their favour.
 * The Battle of Stalingrad, for the German forces in the Soviet Union. So much so that this was the first time the Nazis publicly acknowledged that the war was beginning to go badly.
 * The Second Battle of El Alamein, for the German forces in North Africa.
 * Despite the loss and withdrawal from El Alamein, the campaign in North Africa continued for another six months. When Rommel ordered the retreat, Montgomery did not pursue and thus allowed the broken German formations to withdraw, fortifying themselves within Tunisia. The loss of Tunisia occurred only a few months after the loss at Stalingrad, with a quarter of a million troops taken prisoner. Soon after, the loss of Sicily was so great that the Italians overthrew Mussolini.
 * The Battle of Gettysburg was a major turning point of the American Civil War.
 * Although the war did continue for nearly two years after that. Many however actually see the Battle of Antietam as the real turning point of the war, because this was the last real chance the Confederacy had of not just temporarily carrying the war north (there was also a Southern offensive in the west at the time, while even if Gettysburg had been won by Lee, Vicksburg still would have fallen to Grant), but also to gain recognition from the major European powers.
 * The Battle of the Alamo, which was a major defeat for the Republic of Texas.
 * Subverted and completely reversed in that the Alamo actually fulfilled its objectives. While a tactical defeat, it was a resounding strategic victory that not only severely bled out the Mexican Army and allowed the Texan Army to organize into a fighting force. Also provided substantial morale boost.
 * The men of the Alamo had actually been ordered by Sam Houston to leave--Bowie's men originally came to destroy the fort, but the defenders chose to stay. Perhaps a better example from that war is the Battle of San Jacinto, where the relatively ragtag and much smaller Texan army hid out in the swamplands near what is now Houston, and defeated Santa Anna's men in a completely unexpected attack.
 * Gallipolli for Australia and New Zealand. It's viewed in much the vein as Dunkirk for the UK, only more so.
 * The Battle of Lepanto and the second Siege of Vienna for the Ottoman Empire.
 * The Battle of the Allia for Ancient Rome. The Gaulish chieftain Brennus defeated the Roman army and sacked Rome itself. The Romans were determined never to allow this to happen again, and strengthened the city's defences, reorganised the army and, for generations afterwards, marked the anniversary of the defeat by sacrificing the city's guard dogs as punishment for their failure to alert the Romans to a night attack on the Capitoline Hill. The sacred geese that did alert the Romans were carried through the city on gilded cushions in the same ceremony.
 * Same thing would happen 800 years later in year 410, when the Visigoths under Alaric I sacked Rome. The Roman Empire remained as an independent nation and would live to 476, but it was clear to everyone after the sack that Rome was at that point just a shadow of its former glory self, and the only reason why the Huns were not able to finish the job was because of Flavius Aetius (who historians calls "the last true Roman")' tactical genius and his alliance with the Visigoths.
 * During the Russian Civil War, Kolchak's defeat at Tobol was the turning point for the Whites to start losing. After that defeat, Kolchak's Eastern White army started a retreat that quickly escalated to panicked flight resulting in the fall of Omsk, the rebellion at Irkutsk and Admiral Kolchak's own demise. For Denikin's Southern White army, the failure of his Moscow offensive at the battle of Orel was such a defeat; after Tobol and Orel the Reds had a practically guaranteed win, and the rest of the war was basically cleanup of remnant Whites, Blacks and Greens.
 * The sinking of the SMS Szent István during World War I was this for the Austro-Hungarian Navy. Before that, the Austro-Hungarians had tried various times to break the Otranto Barrage. Then the Szent István, the flagship of the fleet, was sunk by two Italian torpedo boats that just happened to be in the area, and not only the attack the flagship was supposed to lead was canceled, but the Austro-Hungarian navy didn't dare to leave the ports anymore.

Sports

 * The 04 Dream Team during the 04 Olympics, whom were soundly beaten by...Puerto Rico . The media never let them live it down. Until they started curb stomping international teams again.
 * Happened in the NBA with the Goldenstate Warriors knocking off The Dallas Mavericks in the first round of the playoffs!
 * Ice Hockey World Championship, 2003. Finland, who were the tournament's host, had a 5-1 lead over eternal rivals Sweden by the time the second period was half way through. The game ended 6-5 for Sweden.