In case the Ukrainian crisis doesn't scare you enough, consider this from the New York Times:
The Russian occupation of Crimea has challenged Mr. Obama as has no other international crisis, and at its heart, the advice seemed to pose the same question: Is Mr. Obama tough enough to take on the former K.G.B. colonel in the Kremlin? It is no easy task. Chancellor Angela Merkel of Germany told Mr. Obama by telephone on Sunday that after speaking with Mr. Putin she was not sure he was in touch with reality, people briefed on the call said. “In another world,” she said.
http://mobile.nytimes.com/...=
Merkel is not prone to dramatics. The idea that Putin is not in touch with reality frankly scares the living hell out of me. If read the history of WW1 you find that at its core were a series of misjudgments and misreadings of the other sides intention. This is, in fact, how most wars starts. WW2 in this sense is the exception, not the rule.