In all honesty: This is not a topic to do jokes or provoke people for fun. If you think all what is happening right now is funny, you should take some history lessons regarding the Cold War era and educate yourself.
One can only guess why Putin is doing this, but in fact, he had a very reliable lesson on what would happen if he did this. The lesson was called: Syria.
Still, after years of war and murder, Assad is still there. And nothing has happended. After Iraq, no one is interested in another war and will most likely just put up economical restrictions to stop him. Which will do some damage, but not enough to stop him. In addition, Russia could to the same to Europe, when they just close the gas valves. So it's basically a stalemate.
I don't think Putin plans an open combat, he wouldn't have sent soldiers without tags to Crimea in this case. But if it comes to combat, there probably wont be an intervention by the EU/UN. Same with Georgia years ago.
I don't want to judge who is right or who is wrong, but I just hope for the people in the Ukraine that they will not have to suffer more killing and more oppression from any forces.