Humanity first

i read a really cool short story about aliens coming to earth but when they tried to attack it was with muskets and blackpowder
apparently the secret to interplanetary travel was absurdly easy and we just never came across it, so we had the firepower of a galactic superpower confined to one planet

Sounds realistic enough with how we use nuclear energy

the humble planet-sized galaxy obliteration device:

We're too busy invading ourselves to care about green men

And that’s why they’re scared to give us a common enemy

just think how humans changed the earth as a place to live in it