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Tumblr (for once) has a great idea for a sci-fi show.(r/scifi)
Here’s a list of science fiction novels or short stories which use this basic idea that you might be interested in:
The Damned by Alan Dean Foster
Humans are militant badasses in a universe full of squeamish aliens who are worthless at fighting, physically weak, and vulnerable to mind control by the badguys.
The High Crusade by Poul Anderson
Englishmen from the middle ages conquer a technologically sophisticated but militarily incompetent and highly decadent batch of aliens.
The Excalibur Alternative by David Weber
Similar plot as the above.
Ranks of Bronze by David Drake
Similar plot as above but with ROMANS!
Berserker Series by Saberhagen
In a universe full of aliens incapable of committing violence, humans are the only ones capable of fighting off Berserkers robot ships programmed to destroy all life.
World War Series by Harry Turtledove
Technologically and socially stagnant aliens with slightly better than modern technology attempt to invade Earth during WW2–get more than they bargained for from a highly innovative humanity who is twice as tall and has much better cold tolerance.
Rescue Party by Arthur C Clarke
Aliens arrive hoping to save a few humans from an impending supernova, only to find they are too late, and all the humans are mysteriously gone….
With Friends Like These by Alan Dean Foster
Alien federation pays a call to a future Earth to ask for help with an oncoming menace. Sees humans looking peaceful and pastoral at first, but get a surprise….
Pandora’s Planet by Christopher Anvil
The average alien invader is dumb as bricks, compared to humanity. Hilarity ensues.
The Road Not Taken by Harry Turtledove
A universe where most alien species develop anti-gravity and warp drive early on, but this leads them down a dead end and they never get much past black powder and spyglasses. Humans miss the inventions and thus miss the dead end. Spaceships full of musket wielding teddy bears attempt to invade, with predictable results.