The annexation of Crimea guaranteed the long-term security of the Sevastopol base. But that was only one of several concerns for Russia raised by the conduct and composition of the new Ukrainian government. Other equally important concerns remain, and until they are addressed, Russia will continue to apply pressure on Kiev. Given the current and likely future underrepresentation of eastern Ukraine in the central government, Russia insists that Ukraine be transformed from a highly centralized unitary state into a highly decentralized federal state in which the regions control their economy, taxes, culture, language and education.
Dulling Putin's knife and ending the Ukraine crisis peacefully depends largely on the EU. Sanctions will not impress Putin (he and his cronies are isolating Russia economically and financially more effectively than most sanctions could); peaceful yet tangible political steps within Europe will. Polish Prime Minister Donald Tusk has made the right suggestion here: prompt establishment of a European energy union, starting with the market for natural gas and including joint external representation and a common pricing policy. This step, combined with further differentiation among supplier countries and progress toward implementing renewable-energy technologies, would invert the balance of power between the EU (Russia's most important customer for oil and natural gas) and the Kremlin.