Are you talking about the germans in this manga specifically or the entire german Volk? The german state has always been an applicant of realpolitik which in this case would be to leave africa to the africans while conquering the rest of the world and technologically advancing so far that you...
The king should know that africans will never be a real threat to Evropa. Them having 6 japanese teenagers with a bit of modern knowledge wont change that. Letting the blacks have africa and conquering the rest of the world for Germania would be a good compromise.