A look at Ukraine's internal divisions

When Russian troops marched into the Crimean Peninsula over the weekend, it was under the auspices of protecting ethnic Russians living in the area from the freshly installed pro-Western leadership in Kiev. European and U.S. leaders fear that Russian President Vladimir Putin might push further into Eastern Ukraine, a region which still has close ties to its neighbor to the east.

The country is divided by ethnic heritage, language and politics. Broadly, the eastern half is more pro-Russia while the west has sought a closer partnership with Europe, a division at the heart of the protests that ultimately led to the ouster of Kremlin-backed President Viktor Yanukovych.

The borders of what the world knows as modern-day Ukraine were only settled in 1945, after centuries of conflict and war. The western part of the country had a brief flirtation with independence between the two world wars, but was otherwise part of Poland and the Austro-Hungarian Empire. The eastern parts of the country were more closely aligned with the Russian empire for several hundred years before the Soviet Union annexed the entire area after World War II.

Nikita Khrushchev, the leader of the U.S.S.R., gave Crimea to the Ukrainians in 1954 to mark the 300th anniversary of Russia's acquisition of Ukraine in the Treaty of Pereyaslav, cementing the territory that would become an independent Ukraine in 1991 after the collapse of the Soviet Union.

More 90 percent of the eligible voters -- about 84 percent of whom showed up for the 1991 referendum on whether to declare independence -- voted in favor of establishing a separate country, including 54 percent of those in Crimea, despite a large population of ethnic Russians.

Twenty-five years after independence, there's still a strong sense of Russian heritage in the country's east. Nearly 80 percent of the country is ethnically Ukrainian, but Russians make up the next-largest group with 17.3 percent. And ethnic heritage is not black and white: ethnic Russians intermarried with ethnic Ukrainians, but also with Belarussians, Moldovans, Bulgarians, Romanians and Poles, other groups represented in the country. There are also the Crimean Tatars, a Muslim group that makes up just half of one percent of Ukraine's overall population, but 12 percent of Crimea's two million people. They were deported en masse by Joseph Stalin near the end of World War II, but returned once Ukraine became independent -- and feel none of the affinity for Russia that some of their neighbors do.

"This is one of the big blind spots that Moscow has had: in eastern Ukraine you have a lot of people who speak Russian and feel an affinity with Russia... but identify as Ukrainian, see themselves as part of a Ukrainian state and don't want to be swallowed up by Russia," said Jeffrey Mankoff, the Deputy Director of the Russia and Eurasia Program at the Center for Strategic and International Studies. "I think Moscow is making a big miscalculation if it thinks that these people are going to fight on the side of Russia if there's a conflict."

Angela Stent, the Director of the Center for Eurasian, Russian and East European Studies at Georgetown University and a Senior Fellow at the Brookings Institution, noted that even many pro-Ukrainian politicians speak Russian, especially in the capital city of Kiev.

The same goes for ethnicity, even in Crimea, where roughly 60 percent of the residents are ethnic Russian, Mankoff said. "Even among the ethnic Russians its not clear at all any of them actually want to be part of the Russian federation or want Russian protection, and then if you start talking about the rest of eastern Ukraine it goes down from there," he said.

In a May 2013 survey of Crimea, the International Republican Institute found that 53 percent would choose an economic union with Russia, Belarus and Kazakhstan, versus just 17 percent of those who preferred the European Union if just one arrangement was allowed. At the same time, however, a growing number of Crimeans are satisfied with their status as an autonomous region within Ukraine. Fifty-three percent said they preferred the current arrangement, up four points from a similar survey in October 2011, and the number of people who said they believed the peninsula should be separated and given to Russia dropped from 33 percent to 23 percent.

Political differences are less about ideology, and more about identity, Mankoff said. People have tended to make their affiliations based on their location and heritage, which were reflected in the 2010 election. Yulia Tymoshenko, the former prime minister, received more than three-quarters of the vote in the westernmost regions of the country. Yanukovych got his strongest support in the south and east. The areas in the middle of the country were more evenly divided.

CBSNews.com's Alexander Trowbridge contributed to this report