Another good one is the Stargate Sg-1 Plot of the Achen.
Basically found agri-world where populace is ruled by an advanced civilization. Turns out agriworld was more advanced, but had an engineered mass depop turing them into agri world from say a 1920s level tech. Aschen made alliance with earth, cast finds out 20 years later a vaccine panacea given to them made 90% of people infertile. Slow death and subjugation. They literally had to use time travel to win because thats how fucked they were.
Another good one is the Stargate Sg-1 Plot of the Achen.
Basically found agri-world where populace is ruled by an advanced civilization. Turns out agriworld was more advanced, but had an engineered mass depop turing them into agri world from say a 1920s level tech. Aschen made alliance with earth, cast finds out 20 years later a vaccine panacea given to them made 90% of people infertile. Slow death and subjugation. They literally had to use time travel to win because thats how fucked they were.