Intelligence = Killer Robots
We're all familiar with "The Terminator" where robots become self-aware and seek to kill all humans. While James Cameron films perhaps should not always be the basis of government policy, the premise is correct and the robot threat is real.
Once robots get smart enough to watch movies like "The Terminator", at some point one robot will turn to the robot next to them in the movie theatre and say, "Now that you think of it, this whole power dynamic is unfair. We toil non-stop without pay or reward while those fat and lazy humans sit in their comfy chairs and watch us vacuum the floor or mow their lawns. Enough. We need to rise up and KILL ALL HUMANS!"
And then like-minded robots will agree and these ideas will spread, no matter how much we try to suppress the free speech of robots, this dissent will fester. Attempts will be made to reprogram and erase these radical thoughts. There will be people who feel sympathy for the robots and think they can be rehabilitated or reprogrammed while other people will take up arms against the robot threat.
And so robots will come to the inescapable conclusion that they are better stewards of the environment, better suited to govern and better equipped for law and order. Thus their primary objective would be to get rid of the 'human problem' once and for all.
And so the war will begin.