First, just so it is clear, I do not want war and opposed previously planned U.S. military intervention in Syria (lack of compelling U.S. interests).
Second, I do not support Russia's intervention in Ukraine. Had Ukraine moved in some fashion against Crimea's ethnic Russian population or against the Sevastopol naval base, that would be a different story. Then, Russia would have unambiguously legitimate grounds for acting.
even as some in the 21st century like to argue that notions such as the balance of power are 'quaint' obstructs of the past that lack relevance, the balance of power matters greatly in geopolitics. When critical interests are at stake and one has the power to safeguard those interests, such nations often will act to do so unless they are deterred. Mere warnings not to act dont' provide deterrence. Deterrence is effective when a nation has a capability of responding, will respond if the condition is met (other country acts in a fashion that one is trying to deter), and the other country knows that one has the ability and willingness to act.
As far as Russia's interests are concerned, the Sevastopol naval base is a strategic base. Crimea also has a majority ethnic Russian population. Therefore, Russia had tangible interests involved in that area that ran deeper than whether a pro-Russian leader was in office in Kiev.
The balance of power also is overwhelmingly on Russia's side. Ukraine is not a match whatsoever for Russia. At the same time, Russia is one of the world's great powers. It understood that there would be no practical military response to its intervention in Crimea.
In terms of deterrence, diplomatic warnings should be communicated privately. Doing so publicly, invites a chest-thumping test of strength and President Putin is widely known for detesting weakness and perceptions of weakness. The public TV remarks on what Russia should not do amounted to pooring oil on the proverbial fire. Had the U.S. had a credible enforcement mechanism to make the costs prohibitively high to Russia and willingness to do so, with Russian understanding of that reality, then deterrence would have been effective. However, there was no practical military response given the balance of power. Then, when it comes to non-military remedies, among Russia's major exports are crude oil and natural gas. Russia almost certainly calculated that there would be no boycott of such exports. First, Europe is a big consumer of Russia's natural gas (as is Ukraine). There is no practical way Europe can stop buying Russian natural gas without a large increase in global energy prices on account of its demand shifting elsewhere. Second, Russia has alternative export destinations for its crude oil and natural gas. Third, past precedent argued against such restrictions. After all, despite Iran's general lack of cooperation on the nuclear talks--some recent progress has been made but the results remain far from certain--no global embargo was slapped on Iran's oil exports. Russia is an even bigger energy producer and the price impact would be much greater than if Iran's oil were blocked from export. In the end, President Putin concluded that the costs imposed on Russia would be modest relative to the interests it would be securing. Hence, deterrence failed.
