I really wonder if a world war is possible at this stage. What with nuclear weapons, advanced satellites, stealth bombers, the internet... I'm not entirely convinced that a long, drawn-out war with many adversaries is possible anymore.

At the very least, the nationalistic "us vs. them" mentality that was present in the first two world wars would be radically different. For the first two world wars, "the enemy" was more or less a faceless evil across the ocean. Now, with the Internet, literally anyone could go on some website and talk to the people in enemy countries. It would really change things.