If you look at a map of Russia, you can see that its only warm water port is in the Black Sea. Russian military was in the Crimea lawfully until a few weeks ago. Had Putin done nothing, Sevastopol would remain a Russian base. One way to explain what Putin is doing is to conclude he’s just exploiting an opportunity presented by the Maidan and will stop with Crimea. But that ignores geography. Russia can’t rationally expect to hold the Crimea in the context of a militarily hostile Ukraine. Crimea only has roads to the Ukraine: none to Russia. Unless Ukraine capitulates, Putin can’t keep Crimea without forcefully seizing parts of the Eastern Ukraine.
I’ve been wondering where the Russian main battle tanks are because I haven’t seen any in the shots near the Ukraine. Today I saw a post of what was claimed to be a train of Russian main battle tanks in the Crimea. Exactly why the Russians would want their main battle tanks on land that is essentially an island escapes me.