It's not just that Ukraine has two halves that predominantly speak different languages. They have different politics and different visions for their country.
The Russian-speaking, eastern half of Ukraine tends to be, big surprise, more pro-Russian. President Yanukovych is from that part of the country, has most of his support there, and did not even speak Ukrainian until he was in his 50s.
The pro-EU-deal protests have mostly been in the Ukrainian-speaking, western half. That's also the half that voted overwhelmingly against Yanukovych in 2010. (That has been changing since the anti-protest law, which inflamed nationwide anger with Yanukovych.)
This divide has been a challenge for Ukraine since it won independence in 1991. Elections have been near-evenly split between the two halves, pulling the country in opposite directions. As the Ukraine-focused political scientist Leonid Peisakhin put it, Ukraine "has never been and is not yet a coherent national unit with a common narrative or a set of more or less commonly shared political aspirations."
In some ways, this crisis is about popular anger against a president who mishandled the economy and whose attempts to quash protests have edged into authoritarianism. But it's also about Ukraine's long-unresolved national identity crisis. This story is often framed as Ukraine being pulled by Moscow on one end and Europe on the other. But Ukrainians themselves are doing a lot of the pulling: a 22-year tug-of-war between two halves and two identities.
4. Wow. How did Ukraine get so divided?
Ukraine was conquered and divided for centuries by neighboring powers: the Polish, the Austrians and most of all the Russians. But Russian rulers didn't just want to rule Ukraine, they wanted to make it Russian.
The Russification of Ukraine began 250 years ago with Catherine the Great, who oversaw Russia's "golden age" in the late 1700s. At first, she controlled only eastern Ukraine, where she developed vast coal and iron industries to feed Russia's expansion. Though she later took the west as well, she and subsequent Russian rulers focused overwhelmingly on the east, which also happens to be some of the most productive farmland in the world.