Name a case of Mistreatment-Induced Betrayal

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"According to the backstory of Donkey Kong 64, K. Lumsy disliked K. Rool's plan to destroy the island where the Kongs live. In response, K. Rool imprisoned him. Conveniently enough, all of the Kongs' progress occurs as a direct result of K. Lumsy's intervention. Way to antagonize the guy who's about as big as the island you're trying to destroy, K. Rool."

" •Kyle Schneider and Dr. Drago Pettrovich Madnar's reasons for defecting to Zanzibar Land in Metal Gear 2. In regards to Kyle Schneider, he initially supported NATO/FOXHOUND in regards to taking down Outer Heaven, but after Outer Heaven was destroyed, he and his resistance were stabbed in the back so to speak when NATO commenced an air raid that completely and indiscriminately wiped out pretty much a lot of people, and he himself was also captured and experimented upon at NATO for an extraterrestrial special forces project. After traveling to the Mercenary War, he ended up joining Big Boss and Outer Heaven not just due to what NATO did to him, but also because unlike NATO, Big Boss actually saved his resistance as well as the rest of his soldiers. As for Madnar, after defecting to America from the Soviet Union, even abandoning his own daughter, his treatment by the American government and the Scientific Community was... not too good to put it simply. Aside from being ridiculed for his theories about Metal Gear, he also was frequently abused by his superiors and often treated with complete contempt, especially when they only wanted him to make stuff like SDI, NEDW, and brain bombs. Eventually, he had enough and joined Zanzibar Land.
•Although not a direct result of Outer Heaven, it is implied that Gray Fox's defection to Zanzibar Land, aside from his obvious loyalty to Big Boss and his need for war, also came from a Mistreatment Induced Betrayal. While watching the Calgary Winter Olympics in 1988, Gray Fox (living under the paper-thin alias of Frank Hunter [his last name, Jaegar, was German for Hunter]) he ended up falling in love with Gustava Heffner, a ice-skating competitor from Czechoslovakia, and they attempted to elope together, with her attempting to defect to America. Unfortunately, America rejected her request, which also made life a living hell for her and the rest of her family as she was stripped of her competition rights and she and her family was later hunted down. Suffice to say, Gray Fox was not too happy about this at all."

"Cyril from Advance Wars: Days of Ruin. Although he is a clone, he helps the heroes thwart the plans of the Big Bad, while losing his life in the process.
•Earlier on when you rescue Waylon from the Lazurian army, he takes off but his entire unit sticks around (which gives you access to aerial units). They only followed him because they had nowhere else to go, and are more than happy to jump ship to Brenner's Wolves when they hear Brenner isn't a complete dick."

"In Fullmetal Alchemist, Human chimeras Heinkel and Darius join Edward after Kimblee blows up the mine shaft containing all three of them."

LeFou's response to Gaston using him as a shield in the live action Beauty and the Beast?  Turn to the side of the titular duo.