In Ukraine, the West has played—quite disastrously—into Vladimir Putin's hands. The mistakes go back almost a decade. But the most recent one occurred when protesters took to the streets to oppose the Yanukovych government.
The West, by which I mean Nato and the European Union, should have made clear that whatever sympathies they had with the protesters' aims, the right way to change the government was by the ballot box. The failure to do that has provided Putin with the pretext he needed to have Russian forces seize control of Crimea.
Putin's motivating factor is his desire to avenge, what he sees as, the humiliation of Russia at the end of the Cold War. A key part of that for him is reasserting Russia's influence in its near-abroad. He chooses to use defending Russian speakers rather than Russian Orthodox believers as his excuse for interference, but the tactic would be entirely recognisable to Catherine the Great. There's little doubt, to my mind, that if left unchallenged Putin would attempt to create a new Russian empire.
But the West needs to be careful not to play Putin's game. Nato and the European Union should be stressing the need for Crimea to determine its own status through democratic means and for free and fair elections in Ukraine.