Putin's continuous talk in his speech of Russian lands that were taken and are being turned against it makes it sound like this is only the beginning of an attempt to reconquer the former Soviet states. He's daring anyone to stop him on the premise of mutually assured destruction. Which for the first time since WWII has been breached outside of proxy nation wars.
Ukraine is not quite proxy, but it isn't quite a direct NATO alliance attack either. This is probably the biggest international nuclear crisis since the Cuban Missile Crisis
As a history major, I'm really afraid the human race will never learn. The world should take Putins AP statement about things the world has never seen if there is any interference as a madman looking for global destruction.