(CNN) -- Just when it looked like Ukraine was settling down after toppling pro-Russian President Viktor Yanukovych over the weekend, tension flared again in Crimea, the southern part of the country where support for Russia is strong. Armed men seized regional government buildings in Crimea and hoisted the Russian flag.
Rival demonstrators chanted "Crimea is Russia" and "Crimea is not Russia" back and forth at each other.
With the peninsula turning into a flashpoint, here are five things you need to know about Crimea.
1. Crimea isn't legally part of Russia now, but it has been in the past.
Moscow has had an interest in Crimea for hundreds of years, with its rich farmland and its access to the Black Sea. Russia gave Crimea to Ukraine in 1954, when both Russia and Ukraine were part of the Soviet Union.
After the Soviet Union collapsed in 1991, there was some local desire for Crimea to leave Ukraine and become part of Russia again, but lawmakers in Ukraine and Crimea voted for it to stay part of Ukraine.
2. A lot of Russians still live in Crimea.
There are actually three main groups in Crimea: ethnic Ukrainians in the north, Russians in the south, and a third group called Tatars in the middle. The Tatars represent 15 to 20% of the population and suffered badly under Stalin in the Soviet era. They're "deadest against annexation by Russia," Alexander Motyl of Rutgers University told a Council on Foreign Relations audience last week.
3. Part of the Russian Navy is based in Crimea.
Any talk about the importance of Crimea to Russia quickly turns to the Black Sea Fleet. The Russian Navy has had a base at the Crimean city of Sevastopol, on the Black Sea, for 230 years. Ships and subs based there are just north of Turkey and can reach the Mediterranean to influence the Middle East and the Balkans.
An expert at the International Institute for Strategic Studies has been arguing that the importance of the Black Sea Fleet can be overstated. It is the smallest of the Russian Navy's four fleets, and Russia has a Black Sea coast of its own. In fact, Russia is expanding its Black Sea port of Novorossiysk and moving military vessels there, Christian Le Miere argues.
And yet Sevastopol clearly remains significant for Russia. In 2010, Moscow gave Ukraine a good deal on natural gas, partly in exchange for Kiev extending the Russian Navy lease on the base in Ukraine.
4. Crimea has played a vital role in world history before.
Even if you don't know anything else about the Crimean War, you've heard of Florence Nightingale, the founder of modern nursing. It was in the Crimean War in the 1850s that she became known as the Lady with the Lamp, caring for soldiers wounded in the war that Britain, France and Ottoman Turkey fought against Russia.
Generations of British schoolchildren have memorized a poem dating from the war: "The Charge of the Light Brigade," by Alfred Lord Tennyson. The poem commemorates a blunder when British troops attacked the wrong Russian position and were slaughtered, memorialized by Tennyson in the lines: "Theirs not to reason why, theirs but to do and die."
That same battle added a word to the English language: It was called the Battle of Balaclava.
5. And don't forget Yalta, of course.
When World War II was grinding to an end in 1945, the Allied leaders -- U.S. President Franklin D. Roosevelt, British Prime Minister Winston Churchill and Soviet leader Joseph Stalin -- met to divide up Europe. That meeting, which laid the groundwork for the Cold War, took place in the Crimean resort of Yalta.
CNN's Ben Brumfield contributed to this report