Heel Race Turn

Heel Face Turn on an ethnic scale. A faction allied with the enemy joins the heroes' team. A neutral people becomes convinced it has to side with the villains to survive. Truth in Television, as an ethnic group's character is most engineered by its leaders. Argentinians don't wonder where family members went unless General Videla says they disappeared. Russians aren't losing sleep over fear that neighbors will report them without Russia's secret police. Germans aren't stuffing Jews in chimneys without Hitler's influence.

This trope is more often used in realistic settings where there's gray morality, wars are good vs. good, and alignments aren't ethnically based. Settings where this trope won't be seen are where a culture is Always Chaotic Evil or otherwise demonic. Some sultry succubus or burly half-human warrior might have a Heel Face Turn but these characters are rare exceptions.

Anime

 * All Space Battleship Yamato / Star Blazers stories set after the end of the second season portray the
 * Except for the Bolar Wars Extended, a semi-canon webcomic. The Gamilons are on the side of Earth - the Galmans (basically the Ur-Gamilons) aren't.
 * The Zentran / Meltran in Super Dimension Fortress Macross pretty much split. Some stay with Bodolza, while a large chunk side with the humans.

Comic Books

 * Artesia: Each faction in the setting has had previous alliances and works with whoever its current ruler thinks best serves the faction's interest.

Fan Fiction

 * This is one of the main themes of The Urthblood Saga, based on the Redwall series where the line between "goodbeasts" and "vermin" was strongly established and rarely crossed. In it, the titular badger has received a prophecy of a coming dark crisis, and decides to bridge the divide between the two groups by taking vermin under arms and training them to be decent creatures and soldiers, in the hopes of countering it.

Literature

 * At the end of Starship Troopers, it has been revealed that the "Skinnies", the race shown as one of the enemies in the very first combat scene of the book, have allied with Humans against the Bugs. The raid, in fact, was a scare tactic/warning by humans to convince the Skinnies to ditch the bugs.
 * After the first book of the Sword of Truth series, the D'Haran empire become allies, primarily because the protagonist, Richard, turns out to be.
 * The Star Wars Expanded Universe has the Noghri, who were saved by Darth Vader and collectively owed him a debt and became his personal assassins. Then he gave them to Thrawn. Then Thrawn sent them after Leia. The Noghri can tell your bloodline by your scent. Yeah, that went over well.
 * Also happened to the Yuuzhan Vong, after the defeat of their Supreme Overlord and the arrival of Zonama Sekot were taken as proof that their gods didn't actually support their course of action. They show up infrequently in later works, but usually as allies.
 * In The Inheritance Cycle, the Urgals go from fighting in the evil king's armies to joining the side of The Varden.
 * In the original Shannara trilogy the Rock Trolls serve in the evil Warlock King's army in the first book. In the second having realised they were duped they aid the elves in their fight against a demon invasion.

Live-Action Television

 * The Slave Race Jaffa of Stargate SG-1 desert their evil alien masters en masse in the later seasons.
 * In Star Trek: Enterprise, the Xindi's hat is that their "race" consists of several sentient species which did evolve on the same planet. At the beginning of the Xindi arc, the crew of the Enterprise considers all Xindi to be their enemies. But by and by, Archer and co. manage to convince three of the five living Xindi species to do a Heel Race Turn. They help the humans defeating the other two species and preventing the planned Earthshattering Kaboom.
 * And in Deep Space Nine, we have the Cardassians, longtime enemies of the Federation and allied to the Dominion, suddenly switching sides - in the middle of a major space battle - due to the Dominion having just informed the Cardassians they had destroyed a city and killed its two millions inhabitants as reprisal for an act of the Cardassian Resistence.

Video Games

 * in Halo switch sides around the end of the second game.
 * Orcs in Warcraft 3.
 * All that's known about the Vortigants in the first Half Life is that they're invading aliens. In the second game it's revealed that they were confused and enthralled, and are now grateful for the destruction of their puppet leader. By the third, they gather en mass to support Gordon specifically.
 * The Arcadian Empire in Final Fantasy XII. At least in the ending.
 * The Lurkers are brutish Mooks in the first Jak and Daxter; in the second game, they're... not necessarily good so much as oppressed. Brutter and the Lurkers he asks you to save seem pretty grateful, at any rate.

Western Animation

 * In Avatar: The Last Airbender, this presumably happened to  This didn't come out of the blue, though, as