Fighting for earth

Life was good and dandy on earth until it was conquered it around 5 minutes, then this message was broadcasted by the alien's spaceships:

“Greetings humanity, your world has now been conquered by the Quatrih empire, as per our customs when facing low tier civilizations such as yours, we will give your species a last chance at fighting for your freedom, send your finest warriors on top of our mothership and prove your worth.”

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I need to find a better title, the plot is pretty linear, bad aliens invade earth, pew pew humanity fights and we will see where it goes