It's actually going on for awhile, Russia hasn't been happy...

It's actually going on for awhile, Russia hasn't been happy Ukraine wanted to join NATO and that NATO is entertaining the idea. This is understandably so because therein lies the risk of NATO or US putting their anti-ballistic missiles as well as nuclear missiles (the former probably concerns Russia more than the latter) in Ukraine, which really is their front door. Not to mention, the stationing of NATO troops.

But now is a great time for them to act because the majority of Europe's gas supplies come from Russia, and this supply becomes even more critical with global supply chain in tatters (making sourcing of alternative supply even more difficult). Europe's best weapon to deter Russia from attacking Ukraine is sanctions, but during this time the sanction is likely to end up hurting Europe way more than it does Russia.

Time will tell, hopefully diplomatic will triumph over war. With any luck, we may find out this time tomorrow that world peace will be intact and they managed to find an amicable solution.