Independent Social Democratic Party of Germany in the context of Fritz Zubeil

The Social Democratic Party of Germany (German: Sozialdemokratische Partei Deutschlands [zoˈtsi̯aːldemoˌkʁaːtɪʃə paʁˌtaɪ ˈdɔʏtʃlants], SPD [ɛspeːˈdeː] ) is a social democratic political party in Germany. It is one of the major parties of contemporary Germany. Lars Klingbeil has been the party's leader since the 2021 SPD federal Party convention together with Bärbel Bas, who joined him in June 2025. After losing the 2025 federal election, the party is part of the Merz government as the junior coalition partner. The SPD is a member of 12 of the 16 German state governments and is a leading partner in seven of them.

The SPD was founded in 1875 from a merger of smaller socialist parties, and grew rapidly after the lifting of Germany's repressive Anti-Socialist Laws in 1890 to become the largest socialist party in Western Europe until 1933. In 1891, it adopted its Marxist-influenced Erfurt Program, though in practice it was moderate and focused on building working-class organizations. In the 1912 federal election, the SPD won 34.8 percent of votes and became the largest party in the Reichstag, but was still excluded from government. After the start of the First World War in 1914, the party split between a pro-war mainstream and the anti-war Independent Social Democratic Party, some members of which later formed the Communist Party of Germany (KPD). The SPD played a leading role in the German revolution of 1918–1919 and in the foundation of the Weimar Republic. The SPD politician Friedrich Ebert served as the first president of Germany from 1919 to 1925.

The Communist Party of Germany (German: Kommunistische Partei Deutschlands, pronounced [kɔmuˈnɪstɪʃə paʁˈtaɪ ˈdɔʏtʃlants] ; KPD [ˌkaːpeːˈdeː] ) was the major far-left political party in the Weimar Republic during the interwar period, an underground resistance movement in Nazi Germany, and a minor party in Allied-occupied Germany and West Germany during the post-war period until it merged with the SPD in the Soviet occupation zone in 1946 and was banned by the West German Federal Constitutional Court in 1956.

The construction of the KPD began in the aftermath of the First World War by Rosa Luxemburg's and Karl Liebknecht's faction of the Independent Social Democratic Party of Germany (USPD) who had opposed the war and the Majority Social Democratic Party of Germany (MSPD)'s support of it.

The German workers' and soldiers' councils of 1918–1919 (German: Deutsche Arbeiter- und Soldatenräte) were short-lived revolutionary bodies that spread the German revolution to cities across the German Empire during the final days of World War I. Meeting little to no resistance, they formed quickly, took over city governments and key buildings, caused most of the locally stationed military to flee and brought about the abdications of all of Germany's ruling monarchs, including Emperor Wilhelm II, when they reached Berlin on 9 November 1918.

Although the communist Spartacus League and the left wing of the Independent Social Democratic Party (USPD) wanted to set up a system of council communism in Germany, they were a minority in the councils. Most members wanted an end to the war and to German militarism and the establishment of a parliamentary republic dominated by the moderate Social Democratic Party (SPD). Germany's interim national revolutionary government, the Council of the People's Deputies, was initially a coalition of the SPD and the USPD, but in it and in the majority of the other councils across Germany, the SPD was able to keep the far left on the sidelines. During the two large gatherings of workers' and soldiers' councils in Berlin, the voting generally followed the wishes of the SPD leadership. Crucially, and against the will of the radical left, they were able to schedule an election for a national assembly that would allow all Germans to determine the country's future form of government.

The Majority Social Democratic Party of Germany (German: Mehrheitssozialdemokratische Partei Deutschlands, MSPD) was the name officially used by the Social Democratic Party of Germany (SPD) between April 1917 and September 1922. The name differentiated it from the Independent Social Democratic Party (Unabhängige Sozialdemokratische Partei Deutschlands, USPD), which split from the SPD as a result of the party majority's support of the government during the First World War.

Governments led by the MSPD steered Germany through the German Revolution of 1918–1919 and the first years of the Weimar Republic. They followed a moderate course towards a parliamentary system and often used military force against the radical left groups that wanted a soviet style government. The MSPD introduced important social reforms such as the eight-hour workday and early forms of unemployment and health insurance. The party won more votes than any other in the first two national elections.

The Spartacus League (German: Spartakusbund) was a left revolutionary movement organized in Germany during World War I and immediately thereafter. It was founded in August 1914 as the International Group by Rosa Luxemburg, Karl Liebknecht, Clara Zetkin, and other members of the Social Democratic Party of Germany (SPD) who were dissatisfied with the party's official policies in support of the war. In 1916 it renamed itself the Spartacus Group and in 1917 joined the Independent Social Democratic Party of Germany (USPD), which had split off from the SPD as its left wing faction.

During the November Revolution of 1918 that broke out across Germany at the end of the war, the Spartacus Group re-established itself as a nationwide, non-party organization called the "Spartacus League" with the goal of instituting a council republic that would include all of Germany. It became part of the Communist Party of Germany (KPD) when it was formed on 30 December 1918 and at that point ceased to exist as a separate entity.

Walter Ernst Paul Ulbricht (/ˈʊlbrɪxt/; German: [ˈvaltɐ ˈʔʊlbʁɪçt]; 30 June 1893 – 1 August 1973) was a German communist politician. Ulbricht played a leading role in the creation of the Weimar-era Communist Party of Germany (KPD) and later in the early development and establishment of the German Democratic Republic. As the First Secretary of the Communist Socialist Unity Party from 1950 to 1971, he was the chief decision-maker in East Germany. From President Wilhelm Pieck's death in 1960, he was also the East German head of state until his own death in 1973. As the leader of a significant Communist satellite, Ulbricht had a degree of bargaining power with the Kremlin that he used effectively. For example, he demanded the building of the Berlin Wall in 1961 when the Kremlin was reluctant.

Ulbricht began his political life during the German Empire, when he joined first the Social Democratic Party of Germany (SPD) in 1912 later joining the anti-World War I Independent Social Democratic Party of Germany (USPD) in 1917. The following year, he deserted the Imperial German Army and took part in the German Revolution of 1918. He joined the Communist Party of Germany in 1920 and became a leading party functionary, serving in its Central Committee from 1923 onward. After the Nazi takeover of Germany in 1933 and the Nazi-led investigation into his role in ordering the 1931 murder of police captains Paul Anlauf and Franz Lenck, Ulbricht lived in Paris and Prague from 1933 to 1937 and in the Soviet Union from 1937 to 1945.