You may wish to read up on attitudes immediately prior to WWI. And there were three dominate military powers at the start of WWI, Germany the land empire able to call up 5M men in days, Russia with infinite manpower but so logistically messed up they never get to use them, and the British Navy dominated the waves, which was a pretty big deal as this was toward the end of the colonial era (although Germany didn't get to play colonialism which was arguably part of the problem)

Seriously, the franco prussian war was only a couple months adn the protoGermans won decisively. They really did expect to be done, one way or another, by winter time.

WW3 will probably be something like NK implodes and tries to blow up SK and .jp along with it (australia?), and China and "the west" argue very forcibly about who will dominate the area in a post-NK, perhaps post-SK and post-.jp world. At least if I was writing an Alt Hist type novel thats where I'd generally go.