Why were Contra's heroes replaced by robots in Europe?

Europe's Contra, released for the NES on December 28, 1990, is called Probotector, a name built from robot and protector. Bill Rizer and Lance Bean are gone. In their place: RD008 and RC011, combat robots, fighting an enemy force that was likewise robotized wherever the original game had put human soldiers.

The documented reason points at Germany. The federal review board, the BPjM, could place media judged to glorify war or the killing of people on its index. Indexing did not ban a game outright; it did something nearly as fatal to a retail product: no sales to minors, no advertising, no public display. Regional-difference references attribute the robot swap, with a stated presumably, to exactly this: rather than build a Germany-only edition, Konami made the robots the European version, and the whole PAL region got them.

The robots stayed. The European sequels on NES, Game Boy, SNES and Mega Drive kept the Probotector name and its metal heroes into the PlayStation era, while the home computer editions went by Gryzor. And the joke became canon: Contra 4 (2007) hides a Probotector as an unlockable character, written into the fiction as a recon robot sent where humans cannot go.