In 2004, people took to the Maidan Nezalezhnosti, Independence Square, in Kiev, to protest the validity of presidential election results that showed pro-Moscow prime minister, Viktor Yanukovych, winning. The protests became known as the Orange Revolution and brought Viktor Yushchenko to power. Photo: David Guttenfelder/AP
Presidential candidate Viktor Yushchenko listens to his top ally, Yulia Tymoshenko, as he prepares to address supporters in his headquarters in Kiev in November 2004. The two formed a coalition prior to the election. Stepan Chuyko/AP
Ukrainian President Viktor Yushchenko signs an Orange flag, commemorating the first year of the Orange Revolution, in his office in Kiev in 2005. Gleb Garanich/Reuters
The partnership between Viktor Yushchenko and Yulia Tymoshenko quickly unraveled. Here in 2006, former prime minister, Ms. Tymoshenko addresses parliament as her political rivals crowd around the rostrum on the chamber's floor in Kiev. A new coalition headed by Viktor Yanukovych pressed on with its case to form a government after four months of bitter exchanges which pitched the country into political turmoil. Ivan Chernichkin/Reuters
Supporters of Viktor Yanukovych’s Party of Regions shout slogans during a rally in Kiev in 2006. Ukraine’s former Prime Minister Yulia Tymoshenko warned her former ally President Viktor Yushchenko to shun any alliance with Moscow-backed politicians making a comeback after their defeat in the Orange Revolution. Mr. Yushcheko would later appoint Mr. Yanukovych as prime minister. Ivan Chernichkin/Reuters
Judge Suzanna Stanyk of Ukraine’s Constitutional Court is escorted by riot police into the court’s headquarters to start a hearing in downtown Kiev in April, 2007. Thousands of opponents of Prime Minister Viktor Yanukovych blocked the entrances to the court prompting riot police to intervene to allow judges in for the second day of hearings into the legality of a presidential decree dissolving parliament. Sergei Chuzavkov/AP
After more political infighting, Ukraine’s new Prime Minister Yulia Tymoshenko waves after voting in the parliament in Kiev in 2007. Ukraine’s parliament restored Tymoshenko as prime minister, sealing a political comeback for a leading figure from the Orange Revolution three years earlier. Reuters
Ukraine’s President Viktor Yushchenko and first lady Kateryna greet US President George W. Bush and first lady Laura during an official welcoming ceremony in Kiev in April 2008. US President George W. Bush launched talks with Ukraine's pro-Western leaders, determined to press their bid for an early invitation to join NATO despite resistance from the alliance’s European allies. Mykola Lazarenko/Reuters
Orange Revolution opponent and Russian-leaning candidate, Viktor Yanukovych, comes to power after the presidential election in 2010. Supporters celebrate after a hostile presidential election campaign in Kiev, February 2010.
Russia’s President Vladimir Putin (r.) shakes hands with his Ukrainian counterpart Viktor Yanukovych at the Novo-Ogaryovo residence outside Moscow on October 2012. When Yanukovych rejected a trade pact with the European Union and turned to Moscow, he put off painful, EU-prescribed economic surgery that could have hurt his re-election prospects. But he disappointed entrepreneurs who had hoped the EU deal would bring long-term growth. Sergey Ponomarev/Reuters
Demonstrators hold up a flag with the face of jailed former Ukrainian prime minister Yulia Tymoshenko during a protest in Kiev on November 2013. Ms. Tymoshenko was imprisoned under Mr. Yanukovych’s rule over what many felt were trumped up charges. Her release was called for by western powers. Sergei Chuzavkov/AP
Tens of thousands of demonstrators marched through central Kiev on November 2013 to demand that the Ukrainian government reverse course and sign a landmark agreement with the European Union in defiance of Russia. The protest was the biggest Ukraine has seen since the peaceful 2004 Orange Revolution, which overturned a fraudulent presidential election result and brought a Western-leaning government to power. Sergei Chuzavkov/AP
Ukrainian President Viktor Yanukovych, second from left, meets with opposition leaders in Kiev on January 2014 to negotiate a solution to ongoing political crisis. Ukrainian Presidential Press Service/AP
Protesters try to break through police lines near the presidential administration building during a rally held by supporters of EU integration in Kiev, December 2013. Ukrainian opposition leaders called for President Viktor Yanukovych and his government to resign at a rally of about 350,000 people, the biggest protest in the capital Kiev since the Orange Revolution nine years ago. Gleb Garanich/Reuters
Marianna Kvyatkovska (l.) and Alexander Bitkin fashion homemade shin and elbow pads from plastic drainage pipes at their home in Lviv, in Western Ukraine on January 2014. They sent the armor to friends camped out in antigovernment demonstrations in Kiev. Laura Mills/AP
A medic from the anti-government protest camp poses for a portrait with his security guard at the barricades near the site of clashes with riot police in Kiev on January 2014. Ukrainian Prime Minister Mykola Azarov resigned while deputies loyal to President Viktor Yanukovych, acting to calm violent street protests, back-tracked, and overturned anti-protest laws they rammed through parliament 12 days before. Thomas Peter/Reuters
Priests walk between riot police and anti-government protesters at the site of recent clashes in Kiev on February 2014. Konstantin Chernichkin/Reuters
People walk on former Ukrainian President Yanukovych’s countryside residence in Mezhyhirya, outside of Kiev on February 2014. Ukrainian security and volunteers from the Independence Square protesters joined forces to protect the presidential countryside retreat from vandalism and looting. Efrem Lukatsky/AP
Ukrainian opposition leader Yulia Tymoshenko addresses anti-government protesters gathered in the Independence Square in Kiev February 2014. She had only been released from prison hours earlier. Yannis Behrakis/Reuters
Artists from the Russian Black Sea fleet dance and music groups perform for pro-Russian people celebrating in Lenin Square, in Simferopol, Ukraine, on March 2014, the same day as a referendum held over the status of Crimea. Russian troops entered Crimea at the end of February and the referendum that was considered illegitimate by many countries. Max Vetrov/AP
A pro-Russian man carries a Russian flag after breaking into the territory of the naval headquarters in Sevastopol, Crimea on March 2014. Around a dozen Ukrainian servicemen, unarmed and in civilian clothes, walked out of the Ukrainian naval headquarters in the Crimean port of Sevastopol after it was taken over by pro-Russian forces. Baz Ratner/Reuters
Members of a Maidan self-defense unit walk past a burnt building on Independence Square in Kiev on April 2014. The self-defense forces were created by volunteers to provide security for protesters on the Maidan. The units were called, "sotnia," meaning hundreds, with some groups coming from specific cities and one comprised solely of women. Valentyn Ogirenko/Reuters
People block a column of Ukrainian Army combat vehicles on their way to the town of Kramatorsk on April 2014. The central government has so far been unable to rein in the insurgents, who it says are being stirred up by paid operatives from Russia and have seized numerous government facilities in at least nine eastern cities to press their demands for broader autonomy and closer ties with Russia. Evgeniy Maloletka/AP
A pro-Russia supporter reacts outside a trade union building where a deadly fire occurred and pro-Russian protesters were trapped in the flaming building, in Odessa on May 2014. It was the worst incident in Ukraine since the February uprising that ended with the pro-Russian president fleeing the country. Gleb Garanich/Reuters
A pro-Russian fighter holds a gun during a handover of the bodies of Ukrainian troops killed in a plane shot down near Luhansk, at a checkpoint in the village of Karlivka near Donetsk, eastern Ukraine on June 2014. Russia is resuming its military buildup along the Ukrainian border as Ukrainian government forces unleashed a major offensive against pro-Moscow insurgents. Evgeniy Maloletka/AP
A child sits in a car standing in line to cross the border into Russia at the Ukrainian-Russian border checkpoint in Izvaryne, eastern Ukraine, June 2014. Some Ukrainians left amid fighting in eastern Ukraine. Evgeniy Maloletka/AP
A woman cries near her burning house after shelling in the city of Slovyansk, Donetsk Region, eastern Ukraine in June 2014. Residential areas came under shelling from government forces. Both sides have been accused of violating the 10-day cease-fire. Dmitry Lovetsky/AP
A girl says goodbye to her friend, a volunteer, before they were sent to the eastern part of Ukraine to join the ranks of special battalion "Azov," during a ceremony to take the oath of allegiance to Ukraine, in Kiev in July 2014. Sergei Chuzavkov/AP
Ukrainian servicemen take cover after firing a cannon during a military operation against pro-Russian separatists near Pervomaisk, Luhansk region, in August 2014. Maks Levin/Reuters
Forensic experts look at a makeshift marker denoting evidence during recovery work at the site of the downed Malaysian airliner MH17 near the village of Rozsypne in the Donetsk region in August 2014.
Prime Minister Arsenic Yatseniuk has ordered a full security mobilization to prevent 'terrorist acts' from being carried out.
ByRichard Balmforth, Reuters
Ukraine's prime minister warned on Thursday of possible attempts by Russia to disrupt an election in Ukraine this weekend, a vote being held against a background of Russian support for separatist rebels and an unresolved row over gas.