Ukraine's energy dependence on Russia's natural gas is a key factor in Ukrainian politics. CNN's John Defterios explains why.
CNN: Ukraine’s political plays with Russia

Russia's President Vladimir Putin (R) speaks with Ukrainian Prime Minister Mykola Azarov before a meeting of the Supreme Eurasian Economic Council at the Kremlin in Moscow, December 24, 2013. Vladimir Putin said today that the final pieces were in place for the 2015 launch of an economic union with Belarus and Kazakhstan that Moscow hopes can also be joined by Ukraine.AFP PHOTO/ RIA-NOVOSTI/ POOL/ ALEXEI NIKOLSKY