Humans actually got their shit together and started investigating all the alien intergalactic tech that was lying around just waiting to be salvaged and exploited for millennia. As a species, humans may not be as intelligent as Gems – but they learn quickly, and their creativity isn't suppressed by some stupid caste-based system. It didn't take long for them to reverse engineer, understand and even enhance the ancient alien technology. High-tech space travel and weapon systems were developed shortly, and were meant to be used in defence against potential extraterrestrial threats.

And the best course of defence is, of course, offence.

And how convenient it is that some of these potential threats already resided on Earth. Very dangerous potential threats. Who have the ability to take any shape or form, who can bend metal and move entire oceans at will, and whose people already have a history of trying to wipe out humanity and exploit the Earth.

I wonder who are the sentinels in this fucked up timeline. Quartz soldiers, maybe?