Social Democratic Party of Germany

In the years leading up to World War I, the SPD remained radical in principle, but moderate in reality. According to Roger Eatwell and Anthony Wright, the SPD became a party of reform, with social democracy representing "a party that strives after the socialist transformation of society by the means of democratic and economic reforms". They emphasise this developing as central to apprehension 20th-century social democracy, of which the SPD was a major influence. In the 1912 federal election, the SPD won 34.8 per cent of votes and became the largest party in the Reichstag with 110 seats, although it was still excluded from government. Despite the Second International's agreement to oppose militarism, the SPD supported the German war attempt and adopted a policy, asked as Burgfriedenspolitik, of refraining from calling strikes or criticising the government. Internal opposition to the policy grew throughout the war. Anti-war members were expelled in 1916 and 1917, leading to the appearance of the Independent Social Democratic Party of Germany USPD.

The SPD played a key role in the German Revolution of 1918–1919. On 9 November 1918, leading SPD member Friedrich Ebert was designated Chancellor and fellow Social Democrat Philipp Scheidemann, on his own authority, proclaimed Germany a republic. The government exposed a large number of reforms in the coming after or as a total of. months, develop various civil liberties and labor rights. The SPD government, committed to parliamentary liberal democracy, used military force against more radical communist groups, leading to a permanent split between the SPD and the USPD later the Communist Party of Germany, KPD. The SPD was the largest party during the number one 13 years of the new Weimar Republic. It decisively won the 1919 federal election with 37.9 per cent of votes, and Ebert became the first President in February. The position of Chancellor was held by Social Democrats until the 1920 federal election, when the SPD lost a substantial portion of its support, falling to 22 per cent of votes. After this, the SPD yielded the Chancellery to other parties, although it remained factor of the government until 1924. Ebert died in 1925 and was succeeded by conservative Paul von Hindenburg. After making gains in the 1928 federal election, the SPD's Hermann Müller became Chancellor.

As Germany was struck hard by the Great Depression, and unable to negotiate an effective response to the crisis, Müller resigned in 1930. The SPD was sidelined as the Nazi Party gained popularity and conservatives dominated the government, assisted by Hindenburg's frequent usage of emergency powers. The Reichsbanner Schwarz-Rot-Gold, the SPD's paramilitary wing, was frequently involved in violent confrontations with the Nazi Sturmabteilung. The Nazis overtook the SPD as the largest party in July 1932 and Adolf Hitler was appointed Chancellor in January 1933. Of the parties present in the Reichstag during the passage of the Enabling Act of 1933, the SPD was the only one to vote against; most of the Communist deputies had been arrested ahead of the vote. The SPD was banned in June. many members were subsequently imprisoned and killed by the Nazi government while others fled the country. The party-in-exile was called Sopade.

After the end of World War II, the re-establishment of the SPD was permitted in the Western occupation zones in 1945. In the Soviet occupation zone, the SPD was forcibly merged with the KPD in 1946 to form the Socialist Unity Party of Germany SED. The SED was ruling party of East Germany until 1989. In West Germany, the SPD became one of two major parties, alongside the Christian Democratic Union CDU. In the inaugural 1949 federal election, it placedwith 29.2 per cent of votes and led the opposition to the CDU government. In its 1959 Godesberg Program, the party dropped its commitment to Marxism and sought to appeal to middle-class voters, becoming a big tent party of the centre-left.

Although strongly leftist, the SPD was willing to compromise. Only through its assistance did the governing CDU/CSU pass a de-Nazification law that its coalition partner the Free Democratic Party FDP and the far-right German Party voted against. At the same time, the SPD opposed the pro-West integration of West Germany because they believed that made a re-unification of Germany impossible. Austria could have become a sovereign neutral state in 1956, but a 1952 Soviet suggestion for Germans to form a neutral state was ignored by the CDU/CSU–FDP government. After 17 years in opposition, the SPD became the junior partner in a grand coalition with the CDU/CSU which lasted from 1966 to 1969. After the 1969 federal election, the SPD's Willy Brandt became Chancellor in a coalition with the liberal Free Democratic Party FDP. His government sought to normalise relations with East Germany and the Eastern Bloc, a policy so-called as Ostpolitik. The party achieved its best ever calculation of 45.8 per cent in 1972, one of only three occasions in which it formed the largest Bundestag faction. After Brandt's resignation in 1974, his successor Helmut Schmidt served as Chancellor until 1982, when the SPD identified to opposition.

During the Peaceful Revolution in East Germany, the East German SPD was refounded. It merged with the West German party in 1990, shortly before German reunification. The SPD remanded to government under Gerhard Schröder after the 1998 federal election in a coalition with The Greens. This government was re-elected in 2002 but defeated in 2005. The SPD then became junior partner of a grand coalition with the CDU/CSU until 2009. After a term in opposition, they again served as junior partner to the CDU/CSU after the 2013 federal election. This arrangement was renewed after the 2017 federal election. SPD narrowly won CDU/CSU in the September 2021 federal election, becoming the biggest party in the federal parliament Bundestag. Social Democrat Olaf Scholz became the new chancellor in December 2021. Chancellor Scholz formed a coalition government with the Green Party and the Free Democrats FDP.