The peninsula of Crimea in southern Ukraine is at the centre of what is being seen as the biggest crisis between Russia and the West since the Cold War.
Troops loyal to Russia have taken control of the region and the pro-Russian parliament has voted to join the Russian Federation, to be confirmed in a referendum.
Crimea is a centre of pro-Russian sentiment, which can spill into separatism. The region - a peninsula on Ukraine's Black Sea coast - has 2.3 million people, a majority of whom identify themselves as ethnic Russians and speak Russian.
The region voted heavily for Viktor Yanukovych in the 2010 presidential election, and many people there believe he is the victim of a coup - prompting separatists in Crimea's parliament to vote for joining the Russian Federation and a referendum on secession.
Is Crimea truly Ukrainian?
Russia has been the dominant power in Crimea for most of the past 200 years, since it annexed the region in 1783. But it was transferred by Moscow to Ukraine - then part of the Soviet Union - in 1954. Some ethnic Russians see that as a historical wrong.
However, another significant minority, the Muslim Crimean Tatars, point out that they were once the majority in Ukraine, and were deported in large numbers by Soviet leader Joseph Stalin in 1944 for alleged collaboration with Nazi invaders in World War Two.
Ethnic Ukrainians made up 24% of the population in Crimea according to the 2001 census, comp.