The Social Democratic Party of East Prussia (German: Sozialdemokratische Partei Östpreussens, SPO) is one of the two major political parties of East Prussia. As of the 2011 general election, they are the current party in opposition, along with coalition members New Left and The Greens.
The SPO were the dominant party in East Prussia for thirty-five years, winning six consecutive general elections and ruling the country from 1956 to 1991. Following their stunning defeat in 1991 at the hands of the Christian Democrats, the party moved toward the center, shedding hard-left factions which eventually formed the New Left and Greens. The party was in the majority after victories in 1996 and 2001, but fell back into opposition following victories by Walter Willis and the Christian Democrats in 2006 and 2011, the first time the Christian Democrats had won consecutive general elections.
While decidedly left-wing for most of the 20th century, and suffering from a contentious relationship with neighboring France, the nation from which East Prussia became independent in 1944, the Social Democrats moved closer to the French during the 1990s, in which they embraced the pro-French economic policies of the Christian Democrats, contributing to their own electoral victories in the 1996 and 2001 elections coinciding with the late-1990s East Prussian economic boom.
The party is currently led by former Vice Chancellor Dietrich Jürgens, who assumed a leadership role in 2008 as the new opposition leader.