Part of Romania during the interwar period, Moldova was incorporated into the Soviet Union at the close of World War II. Although the country has been independent from the USSR since 1991, Russian forces have remained on Moldovan territory east of the Nistru River supporting the breakaway region of Transnistria, composed of a Slavic majority population (mostly Ukrainians and Russians), but with a sizable ethnic Moldovan minority. Years of Communist Party rule post-independence ultimately ended with election-related violent protests and a rerun of parliamentary elections in 2009. Since then, a series of pro-European ruling coalitions have governed Moldova. As a result of the country's most recent legislative election in November 2014, the three pro-European parties that entered Parliament won a total of 55 of the body's 101 seats. Infighting among coalition members led to prolonged legislative gridlock and political instability, as well as the collapse of two governments, all ruled by pro-European coalitions centered around the Liberal Democratic Party (PLDM) and the Democratic Party (PDM). A political impasse ended in January 2016 when a new parliamentary majority led by PDM, joined by defectors from the Communists and PLDM, supported Pavel FILIP as prime minister. Moldova remains Europe's poorest economy; the country signed and ratified an Association Agreement with the EU in 2014, which fully entered into force in July 2016 after ratification by all EU member states.