It's worth reviewing the run-up to WWI. The pre-WWI model of Europe, an endless struggle between Great Powers which had gone on for a millennium, is Putin's model of the world. That's because it gives Russia a role in the world. As an economic power, Russia is in 12th place, behind S. Korea. In a peaceful, trade-based world, Russia is a bit player. Especially since the price of oil tanked.
Thus the Russian invasion of Georgia in 2008, the annexation of Crimea in 2014, and the war in Ukraine from 2014 to now. Putin's desire to be a player on the world stage drives this.
The post-WWII world was, for a long time, two superpowers with nuclear overkill capability glaring at each other but not doing much. That was surprisingly stable. But it is not, historically, a normal condition.
Right now, it's all too easy to bungle into a major war. Likely possibilities are N. Korea vs S. Korea and the US, China vs. somebody over the South China Sea, and Russia vs. Ukraine heating up.