Tensions are rising in Ukraine after president Viktor Yanukovych left the country. Thousands of protestors fought bloody battles in the capital, Kiev for weeks. They wanted Mr Yanukovych's resignation. Many people were shot dead by riot police. The protestors also wanted economic reforms and closer ties with the European Union. Most people in east Ukraine voted for Mr Yanukovych and lean more towards Russia than the EU. There was little violence there.
The USA said Mr Yanukovych is no longer Ukraine's president. It warned Russia to stay out of Ukrainian affairs, saying: "We strongly support Ukraine's territorial integrity." Fears are that Ukraine could break in two. Pro-Russian separatists are active in the region of Crimea. Gunmen in Russian uniforms were guarding Crimea's main airport. Russia sent 150,000 troops to the Ukrainian border. This made Ukraine warn Russia against "military aggression".