Balablok (1973)

The square people all get along nicely and politely with each other until one day they discover a round person. "It's ball-shaped" think they, and so they rather rudely use it as one. Then more round folk turn up and turn the tables. Next thing it's escalated to an army of squares forming the animated equivalent of a Roman turtle against a load of cannonball shaped round ones. Around and round it goes until there is nothing left but splinters and a rather satisfactory sort of hybrid shape that soon adopts exactly the same attitude to different as we've seen all along. This is clearly a metaphor for how human beings tend to treat those whose appearance is different and in many ways it reminded my of a more aggressive "Mr. Men" cartoon. If you're triangle shaped, then you'd best watch out.