I decided to make a backstory as to how they got there in the first place, being robots and all.
One day, an alien race called the Yarri, who looked similar to us, was facing a disaster, a nuclear war was being waged between two nations, neither wanted to lose, so they kept going, and everything kept getting worse, one nation saw the impending doom for there planet, and they started creating the New Planet Colonization Drones or, NPCD's. The NPCD's were programmed to create new, young Yarri, to colonize the planet, eventually they found a suitbale planet, our planet. They wasted no time in sending the drones. but, things would change in the 10000 or so lightyears it would take to get there, and it did change, humans started to pop up, the humans certainly wouldnt like the NPCD's taking over there planet. the Yarri saw this too late, so they sent a reprogramming signal to tell them "Dont destroy humans"
very unfourtantly part of the transmission got interrupted while it was being tarnsmitted, since the transmission was going only a small bit faster, it took a large part of the journey to reach the NPCD's, who had started developing AI. while the transmissionw s just about to get to them, a star they were passing burst into a supernova, changing them, giving them new objectives, they were now meant to overrun that world, but werent allowed to destroy humans, unless told to, the transmission was recieved just afterwards, saying "Destroy humans".
the NPCD's were delighted to here this, however, the supernova blast warped there CPU's, making them unable to think about advanced math and science, making them exactly as smart as the Humans, they arrived at 1000BC with one mission: destroy humanity.
This is my first ever backstory. so dont expect the best.