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 Dniester River supporting the Slavic majority population, mostly Ukrainians and Russians, who have proclaimed a "Transnistria" republic. One of the poorest nations in Europe, Moldova became the first former Soviet state to elect a Communist, Vladimir VORONIN, as its president in 2001. VORONIN served as Moldova's president until he resigned in September 2009, following the opposition's gain of a narrow majority in July parliamentary elections and the Communist Party's (PCRM) subsequent inability to attract the three-fifths of parliamentary votes required to elect a president. Moldova's four opposition parties formed a new coalition, the Alliance for European Integration (AEI), which acted as Moldova's governing coalition until parliamentary elections were held in November 2010 and a new governing coalition could be formed. Moldova experienced significant political uncertainty in 2009 and 2010, holding three general elections (in April 2009, July 2009, and November 2010) and four presidential ballots in parliament, all of which failed to secure a president.