Here are key facts about the former Soviet republic of Ukraine, which called up its military reservists on Sunday in response to a Russian threat to invade its Crimean peninsula.
The dramatic escalation in the three-month crisis came after pro-Kremlin forces seized control of government buildings in the predominantly Russian-speaking territory, raising the prospect it could break away from Ukraine.
Geography: Ukraine lies in eastern Europe and is sandwiched between ex-Soviet Belarus, Moldova and Russia and EU members Hungary, Poland, Romania and Slovakia.
It covers 603,700 square km (241,500 square miles), and is the second largest country in Europe after Russia.
Map of Ukraine's regions identifying the levels of anti-government protests pic.twitter.com/aeT32Y8xA3— Agence France-Presse (@AFP) January 26, 2014
Population: 45.6 million in 2012 (World Bank). Russians make up the largest minority.
History: Much of modern-day Ukraine was part of the former Russian empire although its northwest belonged to the Austro-Hungarian empire. After the Russian revolution, Ukraine became part of the USSR.
Growing opposition to Soviet rule culminated in the declaration of independence on August 24, 1991, confirmed by referendum on December 1.
The world's worst civilian nuclear accident took place in Ukraine on April 26, 1986, at the Chernobyl nuclear power station. Thirty people were killed in an explosion and a further 2,500 died of related illnesses. The reactor was closed in 2000.
Political situation: A 2004 election pitted pro-Western Viktor Yushchenko against pro-Russian Viktor Yanukovych. After official results showed Yanukovych had won, Yushchenko launched mass protests, claiming the election was rigged.
The supreme court agreed and ordered a re-run ballot on December 26, 2004, which Yushchenko won amidst what became known as the Orange Revolution.
But amid huge disappointment with the results of the revolution, Yushchenko was bundled out of the 2010 vote in the first round by Yanukovych, who went on to win against prime minister Yulia Tymoshenko. She was later sentenced to seven years in prison for abuse of power in connection with Russian gas contracts.
In December, protestors angry at Ukraine's decision to suspend partnership talks with the European Union launched a movement of mass protests, which culminated in February with the ouster of Yanukovych.
As the president fled, Tymoshenko walked free on February 22 and her right-hand man Oleksandr Turchynov was designated interim leader ahead of early elections set for May 25.
Economy: In 2013 Ukraine faced an economic crisis and is teetering on the brink of bankruptcy, according to analysts. Gas has been a bone of contention between Russia, which provides 60 percent of Ukraine's needs, and Ukraine which is the main transit country for gas exported to the EU.
In December Yanukovych secured a $15-billion bailout deal from Moscow, and a huge price cut for Russian gas. But Moscow cancelled that deal after only $3 billion had been disbursed, following the overthrow of Yanukovych.
International lenders are currently in talks to muster a financial rescue worth some $15-billion for the country, which has little cash in its coffers and dwindling foreign exchange reserves.