Imperial Rome enslaved the martians, and as a result creates an entire lower caste of space laborers. Over time they could not adapt to earth and their species went extinct. This resulted in the dark ages.

I want to believe

Oops, slave labor. My iPhone typing skills leave something to be desired apparently...

Auto-correct of slave, I imagine. Unless we believe in ancient aliens.

My guess is autocorrect for "slave labor"

Probably slave labor typo + autocorrect