The Joining

The Joining are an militant race of machines.

Culture and society
The Joining are all linked together, sharing a single consciousness across multiple robotic bodies ("like one huge robot, as big as a city"). Whenever they arrive on a new planet, they target the spots where the most advanced technology is being created and abduct locals to be replaced with robotic replicas.

History
According to the Martian Manhunter, the Joining destroyed the race that created them, and since then have launched a campaign of assimilation of technology and knowledge, ravaging half the galaxy. Eventually, they made their way to Earth, causing immense destruction.

The Joining were supposedly destroyed after Batman initiated a fail safe protocol within the technology they stole from Wayne Industries. The Joining however did not give up and with the help of Dr. Hugo Strange, consumed the powers of the Justice League. After the heroes took back their powers, the devised a way to shut them down using Hugo Strange who assimilated their entire knowledge.