The Social Democratic Party of Germany (German: Sozialdemokratische Partei Deutschlands, SPD) is a social-democratic political party in Germany. The party, led by Andrea Nahles since 2018, has become one of the two major contemporary political parties in Germany, along with the Christian Democratic Union (CDU). The SPD has governed at the federal level in Germany as part of a grand coalition with the CDU and the Christian Social Union (CSU) since December 2013 following the results of the 2013 and 2017 federal elections. The SPD participates in 14 state governments, seven of them governed by SPD Minister-Presidents, and as such holds the distinction of being the only political party in Germany represented in all sixteen Landtags.
The SPD is a member of the Party of European Socialists, and initiated the founding of the Progressive Alliance international for social-democratic parties on 22 May 2013, after criticising the Socialist International for its acceptance of authoritarian parties. Established in 1863, the SPD is by far the oldest extant political party represented in the German Parliament and was one of the first Marxist-influenced parties in the world.
The General German Workers' Association (Allgemeiner Deutscher Arbeiterverein, ADAV), founded in 1863, and the Social Democratic Workers' Party (Sozialdemokratische Arbeiterpartei Deutschlands, SDAP), founded in 1869, merged in 1875, under the name Socialist Workers' Party of Germany (Sozialistische Arbeiterpartei Deutschlands, SAPD). From 1878 to 1890, any grouping or meeting that aimed at spreading socialist principles was banned under the Anti-Socialist Laws, but the party still gained support in elections. In 1890, when the ban was lifted and it could again present electoral lists, the party adopted its current name. In the years leading up to World War I, the party remained ideologically radical in official principle, although many party officials tended to be moderate in everyday politics. By 1912, the party claimed the most votes of any German party.
Despite the agreement of the Second International to oppose the First World War, the SPD voted in favor of war in 1914. In response to this and the Bolshevik Revolution, members of the left and of the far-left of the SPD formed alternative parties, first the Spartacus League, then the Independent Social Democratic Party of Germany (USPD) while the more conservative faction was known as the Majority Social Democratic Party of Germany (MSPD) After 1918 the SPD played an important role in the political system of the Weimar Republic, although it took part in coalition governments only in few years (1918–21, 1923, 1928–30). Adolf Hitler prohibited the party in 1933 under the Enabling Act – party officials were imprisoned, killed or went into exile. In exile, the party used the name Sopade. The SPD had been the only party to vote against the Enabling Act (while the Communist Party was blocked from voting).
In 1945, the allied occupants in the Western zones initially allowed four parties to be established, which led to the Christian Democratic Union, the Free Democratic Party, the Communist Party of Germany, and the SPD being established. In the Soviet Zone of Occupation, the Soviets forced the Social Democrats to form a common party with the Communists (Socialist Unity Party of Germany or SED). In the Western zones, the Communist Party was later (1956) banned by West Germany's Federal Constitutional Court. Since 1949, in the Federal Republic of Germany, the SPD has been one of the two major parties, with the other being the Christian Democratic Union. From 1969 to 1982 and 1998 to 2005 the Chancellors of Germany were Social Democrats whereas the other years the Chancellors were Christian Democrats.