People shit on nationalism, patriotism, religion etc but in a society where these are on the decline, the will to defend others at the cost of own safety and prosperity (the so called self righteousness) will disappear. So first the nations will just fend for themselves, then the factions inside the countries and the people themselves. Unfortunately, not engaging is never a great strategy. It's a strategy that looks great but it always makes things worse. The current escalation is solely due to how weak USA looked during their hasty retreat from Afghanistan.

My guess is that Putin just wanted to scare a few people and may be annex the rebel areas. But the weak response has encouraged him to see how far this can be taken. When will the current DefCon change? He would continue till that happens. It's not because he is stupid or crazy. It's a decent strategy to see where the opponents limits for patience are. He would turn around the moment there is some ground action or strict measures like announcing a no fly zone over Ukraine enforced by NATO. Till, then the smart move would be to push forward in Ukraine.