A timeline of events in Ukraine's political crisis during the last several months:
Nov. 21: Ukrainian President Viktor Yanukovych's government announces it is abandoning an agreement that would strengthen ties with the European Union. It seeks closer cooperation with Moscow. Protesters take to the streets.
Dec. 1: A protest attracts about 300,000 people at Kiev's Independence Square. Activists seize Kiev City Hall.
Dec. 17: Russian President Vladimir Putin announces Moscow will buy $15 billion worth of Ukrainian government bonds and all for a cut in the price Ukrainians pay for Russian natural gas.
Jan. 22: The first protest deaths. Two die after being hit with live ammunition and the third after a fall during a confrontation between police and demonstrators manning barricades.
Jan. 28: The prime minister resigns and the parliament repeals harsh anti-protest laws.
Feb. 16: Opposition activists end their occupation of Kiev City Hall in exchange for release of all jailed protesters.
Feb. 18: Street clashes erupt, leaving at least 26 dead and hundreds injured.
Feb. 22: Yanukovych flees the country after a political coup. Opposition leader Yulia Tymoshenko is released from prison.
Feb. 23: The last day of the Sochi Olympics.
Feb. 24: Ukraine's interim government and president, Oleksandr Turchinov, issues a warrant for the arrest of Yanukovych.
Feb. 25: Pro-Russian protesters take a stand in Crimea. Yanukovych's former chief of staff is wounded by gunfire and hospitalized.
Feb. 26: Amid clashing protesters in Crimea, Putin orders military exercises in western Russia. Secretary of State John Kerry vows $1 billion in loan aid to Ukraine.
Feb. 27: Yanukovych surfaces in Russia, appearing for the first time since fleeing Ukraine. Russian jets are on standby in case of combat.
Feb. 28: Armed men in Russian military uniforms take control of key airports in Crimea. Russian marines surround a Ukraine coast guard base in Sevastopol. Obama warns "there will be costs" for Russian military intervention in Ukraine.
March 1: Ukraine's parliament asks for an emergency meeting with the U.N. Security Council. The Ukraine government calls on Russia to put a stop to the "provocations" in Crimea.
March 2: Armed men in trucks and armored vehicles surround a Ukrainian military base in Crimea. Putin tells President Obama that use of force on Russia's part would be a response to provocations from Ukraine.
March 3: Kerry travels to Ukraine.
March 4: In Kiev, Kerry offers the $1 billion loan guarantee and technical experts to help recover assets, referring to the billions reported to have been funneled out of the country by Yanukovych. Putin says he has no intention to "fight the Ukrainian people."
March 5: A special U.N. envoy cuts short its mission in Crimea after a group of armed men order them to leave the region, according to U.N. officials.
March 6: Crimea's local parliament, which largely supported Yanukovych, voted on Thursday to join Russia and scheduled a referendum for March 16 to do that or enact more autonomy from Kiev.
Obama seeks visa restrictions and economic sanctions on Russians who have been involved in military action in Ukraine. The House Foreign Relations Committee calls on Obama to enact financial and trade sanctions against Russia.
March 7: Rallies in the streets of Russia urge Crimea to become part of Russia. A leader of Russia's parliament pledged to support a referendum – deemed illegal by the West – to break from Ukraine.
Ukraine competes in the Winter Paralympics in Sochi despite Russia's military moves in Crimea.
March 12: Obama met Ukraine's interim Prime Minister Arseniy Yatsenyuk. Afterward, Obama said elections could "lead to different arrangements over time with the Crimean region. But that is not something that can be done with the barrel of a gun pointed at you."
March 16: Residents of Crimea, up to 60% percent of whom are Russian, were given a choice of either joining Russia or opting for more autonomy from Ukraine under the 1992 constitution. The status quo, in which Crimea is a semi-autonomous region of Ukraine, was not an option. They voted overwhelmingly to join Russia.
March 17: President Obama announced new sanctions Monday against seven Russian officials. The sanctions focus on the individual personal assets, but not companies that the officials may manage on behalf of the Russian state.
Additionally, Russian President Vladimir Putin officially recognized Crimea Monday as a sovereign independent state, the ITAR-Tass news agency reported.
March 18: Hours after Vladimir Putin and Crimean leaders signed a treaty that makes Crimea part of the Russian Federation, a Ukrainian officer was shot and killed when a gunman attacked a military base near the region's capital. As a result, Ukrainian authorities authorized soldiers to shoot in self-defense.
Sources: USA TODAY, Associated Press