Wayback Trip

So, you've got your time machine and you're merrily having adventures through time and space. And, when you arrive in Ancient Rome, it turns out that a clan of half-werewolf half-vampire techno-sorcerers are attempting to take control of the Senate from within! You have to stop them!

...but wait a minute. The vampwolf sorcerers didn't get to Italy in 326 BC by Time Travel; they've apparently been there all along. So, if you interfere, won't you be changing history? Why isn't Romulus Alucard Caesar in the history books you studied?

Well, maybe it's a Stable Time Loop, and the timeline you know only exists because you were there with silver garlic in Rome. But wait, weren't you worried about changing history just last week? Didn't your traveling companion prevent you from killing Hitler to avoid a Temporal Paradox? So what makes this any different?

When history has changed, and the protagonists must fix it, but there's no reason for it to have changed, that's a Wayback Trip. Unlike Set Right What Once Went Wrong, where the time travelers go back and defeat the villain, and as a result, history is changed for the better, in this trope, the time travelers go back and defeat the villain, and as a result history stays the same. The ultimate result is then either a Stable Time Loop (Rome always had secret lycovamps all along) or a "Close Enough" Timeline, perhaps in which the protagonists Tricked-Out Time (there were no monsters the "first time around", and the second time, there were but no one will be the wiser).

This trope seems to derive from the Adventure Towns treatment of Time Travel. Periods of history are treated like places rather than points on a timeline. New York in 1897 isn't the cause of New York in 2007, it's just 110 years down the road, and is free to have its own history and events.

This could technically be considered a case of Make Wrong What Once Went Right and Terminator Twosome, in that the protagonists are changing history to make their (that is, our) timeline happen instead of the one with Roman vampire werewolf sorcerers.

Can be justified Handwaved by having a Delayed Ripple Effect.

See also Meanwhile in the Future. Compare to Excellent Adventure.

Anime and Manga

 * In one episode of Wandaba Style, the girls accidently travel to the past, when Teen Genius Susumu was a mere Child Prodigy. While there, they encourage him to follow his dreams, and even act as guinea pigs for toned down versions of experiments he'll run in the future, yet when they return to the present, nothing at all has changed.

Comic Books

 * The Dallas arc of The Umbrella Academy has this going on.

Film

 * This trope is the basic premise of the Terminator movies (even though side effects cause some ontological paradoxes).

Live-Action TV

 * Doctor Who does this all the time, especially in the new series. It was pointed out by Martha in "The Shakespeare Code". The Doctor explained that it was similar to Back to The Future. Except this doesn't make sense either; in BttF, Marty was the one who altered history, whereas in the episode, the witches existed totally independent of the Doctor's travels. The general Hand Wave is that things have gotten really screwy since the Time Lords died off.
 * In the original series serial "Pyramids of Mars", Sarah Jane asks why they have to stop the villain destroying the Earth in 1915, when they know it's fine in 1980. In reply, the Doctor takes her to 1980... and it turns out to be a desolate wasteland. Apparently, once the Doctor arrives somewhere, he must complete the Stable Time Loop to maintain the "proper" version of history. (In which case, one wonders... and this question has been voiced in the series... why the heck does the Doctor keep traveling around?! Arguably, if he didn't, the effect would be that 1980 Earth had always been a desolate wasteland, and there wouldn't be a "real" 1980 for Sarah to come from) In Blink, the Doctor explains that time, rather than being a linear chain of cause and effect, is actually "a big ball of wibbly-wobbly, timey-wimey stuff." This apparently explains everything.
 * The new series has also introduced the idea of "fixed points", which amounts to there being some things you can change, and some things you can't.
 * Every episode of Voyagers! The series did mention "the flow of history being tampered with", implying that the changes were caused by other time travellers.
 * The objective of the game show Where In Time Is Carmen Sandiego?
 * The TV series Quantum Leap.
 * In one episode, Sam leaps into various points of Lee Harvey Oswald's life. As it turns out, in the "real" history, Jackie was killed too.

Video Games

 * In Chrono Trigger if you visit the pre-historic time period, and then beat the game without causing the humans to defeat the Reptites, will give you an ending where the Reptites became the dominant species on the planet. However, beating the game before landing in that time period, that future doesn't come to pass, implying that simply landing in the past causes the Reptites to win.
 * In fact, the "World of Reptites" ending isn't caused by the landing in the past, but by the fact that to beat Lavos at this moment, you'll have to take Ayla with you; and, since she's the most skilled human fighter and the only one who would attack the Reptite headquarters...
 * Also, it is implied that the Gate Key incident may have motivated the Reptites to attack Laruba village and get very serious. If Crono and co. never arrived in 65 million BC, that never would have happened.
 * The main plotline of Mario & Luigi: Partners In Time. Aliens invade the past Mushroom Kingdom, causing mass destruction and taking over the castle... but the only effect this has on the present Mushroom Kingdom is the time portals that suddenly appear in the otherwise-intact castle.
 * Technically, the time holes appeared due to an unrelated event that was nonetheless destined to happen so that the bros could travel back in time in the first place. Specifically, from timey machine go boom.
 * In the various Caverns Of Time instances in World of Warcraft, the players' goal is preserving some event in Azeroth's history the way it should be, by defeating The Infinite.

Web Comics

 * "The Stormbreaker Saga" in Sluggy Freelance involves Zoe and Torg going back to medieval times and stopping the demon K'Z'K (who they blasted into the past in an earlier arc) from conquering the world. How this works in terms of a Stable Time Loop or Delayed Ripple Effect is made more confusing by this strip, which thankfully invokes Bellisario's Maxim to Lampshade it.
 * Zoe also claims that the answers to her history test changed over night, with the new answers being in line with her experience in the past. The internal consistent theory of time travel is not revealed to the readers. (If there is one.)

Western Animation

 * The trope name comes from Peabody's Improbable History, a segment on Rocky and Bullwinkle. In every episode, Peabody and Sherman would visit a historical personage with some problem that kept them from doing what they were supposed to do historically, and help them with it.
 * In the first appearance of this segment, it is explained that a straight-up Time Machine is actually rather boring since not everyone in the past is famous. So, Mr. Peabody invented a "Should-Have-Been" machine to ensure that his trips will be interesting rather than historically accurate. (Which leads to Unfortunate Implications when they meet Native Americans and convince them to let the European colonizers win.)
 * Time Squad had a similar gimmick; they lampshaded it through Nonsenseoleum by saying that, in the future, time has gotten old and worn-out, so somebody has to patch it up.
 * Time travel in Gargoyles works like this. In the first episode to feature it (Vows) Demona shows her younger self the future destruction of the clan. Young Demona rebels and Goliath takes the time travelers back to the present, where nothing has changed. The older Demona confesses that she remembers the night very well and it was that fear that motivated her to do what she did. In another episode (Future Tense) Goliath is able to realize that it is All Just a Dream because everyone else is trying to convince him that time travel will fix the horrible future they have landed in.