Don't guarantee things, professor, especially not things of the future.
This isn't 1938.
We have measures in place, that did not exist in 1938. Putin is not Hitler. Ukraine is not Austria.
Just because observers and analysts have drawn these paralels, that is all they are, just paralels. It doesn't mean Putin is sitting around seeking to replicate Hitler step by step, "First we take Crimea, then we take Berlin >:0"
Maybe you weren't talking about these comparisons in particular, and refering to the fact that Ukraine has refused legitimacy to the upcoming referendum, and that annexation would signify a hostile Russian action - but then again, what's the difference between then and now? If Ukraine plans to actually _attack Russia_, why wait untill a date that everyone can guess? They would basically be walking into a meat grinder.
I'm not gonna guess what's gonna happen, cus I don't know. Least of all am I gonna try to guarantee what happens