After World War 3 has devastated the planet and war is outlawed, the remaining civilizations decide that the best use of their limited resources is to have giant fuck-off robots punch each other over territory disputes.
Movie Mastery – Robot Jox (1989)
System Mastery 
Fun new info on this movie, It has bean announced that it will be one of the movies riffed on the now upcoming 13th season of Mystery Science Theater 3000.