Wikipedia:

The German Revolution or November Revolution (German: Novemberrevolution) was a civil conflict in the German Empire at the end of the First World War that resulted in the replacement of Germany's imperial government with a republic. The revolutionary period lasted from November 1918 until the establishment in August 1919 of a republic that later became known as the Weimar Republic.
The roots of the revolution lay in the German Empire's defeat in the First World War and the social tensions that came to a head shortly thereafter. The first acts of revolution were triggered by the policies of the German Supreme Command and its lack of coordination with the Naval Command. In the face of defeat, the Naval Command insisted on trying to precipitate a climactic battle with the British Royal Navy by means of its naval order of 24 October 1918. The battle never took place. Instead of obeying their orders to begin preparations to fight the British, German sailors led revolts in the naval ports of Wilhelmshaven on 29 October 1918 and Kiel in the first days of November. These disturbances spread the spirit of civil unrest across Germany and ultimately led to the proclamation of a republic on 9 November 1918. Shortly thereafter, Emperor Wilhelm II abdicated his throne and fled the country.
The revolutionaries, inspired by socialist ideas, failed to hand over power to Soviet-style councils as the Bolsheviks had done in Russia, because the leadership of the Social Democratic Party of Germany (SPD) opposed their creation. The SPD opted instead for a national assembly that would form the basis for a parliamentary system of government.[1] Fearing an all-out civil war in Germany between militant workers and reactionary conservatives, the SPD did not plan to strip the old German upper classes completely of their power and privileges. Instead, it sought to integrate them into the new social democratic system. In this endeavour, SPD leftists sought an alliance with the German Supreme Command. This allowed the army and the Freikorps (nationalist militias) to quell the extreme leftist Spartacist uprising of 4–15 January 1919 by force. The same alliance of political forces succeeded in suppressing uprisings of the extreme left in other parts of Germany with the result that the country was completely pacified later in the year 1919.
Elections for the new Weimar National Assembly were held on 19 January 1919. The revolution ended on 11 August 1919, when the Weimar Constitution was adopted.