It's possible, but hard, to avoid the civil war. Beyond that, anything is really down to the skill of the player. Nothing is hard coded, the odds are just stacked heavily against Germany (they usually get a civil war including mass rebellion across their eastern territories, the industry and military they are up against is much bigger than them, the western powers could attack them during the civil war or otherwise). Really in a game like HOI4, it's just down to the skill and knowledge of the player, unless you literally hard code them to lose. I mean, people have done Luxembourg world conquests in HOI4, so you see what I mean.