I cannot pretend to have any idea of what has been passing through the head of Vladimir Putin lately, but if he took off his shirt and rode into eastern Ukraine on a horse, I would not be especially surprised. In the meanwhile, though, I figured I could point out a few things that are getting scant notice in the media.
It was during the Crimean War that the 600 rode into the "valley of death," because "someone had blundered." So much for early history: fast forward to 1954. That was the year that Nikita Krushchev gave the Ukrainian SSR "power" over the peninsula, not that it much mattered, because they all were SSRs anyway. When the Soviet Union decomposed, there were some problems working out the differences between the majority Russian Crimea and the rest of Ukraine.
Hence, Crimea is a "semi-autonomous" region, hosting Russian naval bases and, so it seems, some ground forces flown in for the occasion. If it became entirely autonomous (that is, independent), Ukraine would lose most of its major ports — not that it's exporting much, except to Russia.
Ukraine's most significant geopolitical importance is as a place where Russian petrochemical pipelines cross over to the rest of Europe. Since a Russian invasion of eastern Ukraine would inevitably shut down those pipelines, it would create problems for everybody outside the Persian Gulf. Russia's economy, already in bad shape, depends on commodity exports. Without oil and gas exports, it would collapse. Western Europe (including Germany) would slide back into recession.
It would not be such a bad thing if the new (and mostly illegitimate) government of Ukraine let Crimea have its independence following the plebiscite the Crimean leadership is sponsoring. If they wanted "pan-European" trade, it could be done by rail.
Well, at least the Ukrainians are not killing each other — okay, not much — as compared to ethnic/language/racial groups in other parts of the world. Yes, Obama will take shit for "doing nothing," but nothing seems like the best alternative right now.