If you look at the cause of war you will see most are accidents. Under estimating your opponents. This was the case in WW1 where all nations under estimated the other. WW2 was started when Hitler underestimated Britain support for Poland. I think Putin understands Obalma. He knows he can take Crimea without response, Like Crechoslovakia in ww2 but if he go further he will have war.
I doubt if either Putin or Obama will make that mistake.
I doubt if either Putin or Obama will make that mistake.