At a news conference March 4, Putin denied that Russian troops had invaded, despite photographic evidence to the contrary. “You can go to a store and buy a uniform,” insisted Putin. This “deniability” was maintained by Defense Minister Sergei Shoigu, who said on March 5 it was “complete nonsense” that Russian troops had invaded Crimea and that he had “no idea” how Russian military vehicles had gotten there.
These bland denials of reality were useful in several ways: They maintained a fig leaf of legitimacy for an illegal intervention; they allowed Russia a chance (not yet taken) to de-escalate an operation that hadn’t officially been acknowledged; and they distanced Putin in case things went badly and Ukrainians were killed.
Putin also showed a notable willingness to take risks. So far, there has been almost no bloodshed between Russians and Ukrainians, but Putin couldn’t have known this when he began. That’s why the precision and discipline of Russian forces were crucial. Their professionalism reduced the risk of an incident that could have spiraled out of control.
Finally, Putin prepared a rationale for his intervention — along with the attendant propaganda.
I would add that the Western, and particularly the American response, was slow and largely disinterested.
What happens next might be determined by the domestic response in Crimea. Will the Ukrainian and Tatar minorities begin a resistance campaign against their new rulers, or will they keep their heads down and acquiesce? Even low-level violence might keep Putin too busy to take his next bite later rather than sooner. A peaceful transition would make dislodging Russia all but impossible, and also encourage similar actions by Moscow in eastern Ukraine and perhaps elsewhere.