If the Russians invaded the Ukrainian armed forces would probably resist in an organized fashion. In 2008 Russia had a hard time scrounging up enough troops to invade Georgia. But Ukraine has more ten times the population of Georgia and Russia still has a largely dysfunctional armed forces with fewer than 100,000 troops (paratroopers and special forces) that they can really rely on. Russian military staffs are quite good at calculating the “correlation of forces” for an operation and predicting the probability of success and that math does not look good when it comes to invading Ukraine.
What gives Russians pause is the fact ... the Ukrainians are still willing to fight and this time around you cannot keep the barbaric tactics used to suppress the rebellion out of the news.
2. Money in the pocket persuades people. The Ukraine or most of it will be looking west.
When the Cold War ended in 1991 Ukraine and neighboring Poland (both, until then, subjects of Russia) had the same (low) per-capita GDP. Since then Ukrainian per-capita GDP has declined 22 percent while Poland, which quickly developed economic and political ties with the West after 1990, has soared to the point where Polish per capita GDP is three times that of Ukraine. Put simply, most Ukrainians see links to the West as the key to economic growth and protection from Russian domination.3. Fracking is changing politics. The Ukraine is within ten years of energy independence from the blackmail of Russia.
The above is from StrategyPage's "Russia: Fracking to Free Ukraine". You can subscribe to a cheap daily newsletter from them. For the price, nothing compares for deep background from a Machiavellian perspective.
Ukraine began 2013 by signing a $10 billion contract with a major oil company to develop shale gas fields in Ukraine. Within a decade this could eliminate the need to import natural gas from Russia. This would free Ukraine from Russian threats to halt gas shipments if Ukraine did not do as it was told.
The West can .. impose sanctions, which will hurt the Russian economy and the popularity of the current Russian government. Such sanctions are possible largely because of the development of fracking in the United States, which has enormously increased oil and gas production in North America and made Russian oil and gas less of a necessity to the West. It comes down to how much empire can Russia afford. Not much, especially when you own general staff tells you that there are not enough reliable troops to successfully invade Ukraine.
Footnote 1: News stories that say Yanukovych had removed himself to the cityof Kharkiv don't come into perspective until you see the map. It's as close to Russia as you can get and still be in the Ukraine.
Footnote 2: Russia has a great naval base at Sevastopol. This involves Russian property and not just prestige. If the Ukraine handles this like Cuba did Guantanamo Bay, that will tone down aggression. (Update Feb. 27: News stories about armed pro-russian men at the airport in the Crimea point to this being the area where Russia can gain the most benefit with the least effort.)
Footnote 3: Conrad Black's article in the National Post makes clear how complex the past of this region is.
UPDATE: Russian troops are in the Crimea and possibly digging trenches at the neck between Crimea and the rest of the state. My footnote 2 should have been THE LEDE. I think the correlation of forces is still correct as to the country as a whole. An excellent read from Michael Totten who DID predict the absorption of Crimea back into Russia is here.
UPDATE: The Crimea depends on the rest of Ukraine for power and food. Hmmm.