The Free City of Danzig was a city-state under the protection and oversight of the League of Nations between 1920 and 1939, consisting of the Baltic Sea port of Danzig and nearly 200 other small localities in the surrounding areas. The polity was created on 15 November 1920 in accordance with the terms of Article 100 of the 1919 Treaty of Versailles after the end of World War I.

The Treaty of Versailles was a peace treaty signed on 28 June 1919. As the most important treaty of World War I, it ended the state of war between Germany and most of the Allied Powers. It was signed in the Palace of Versailles, exactly five years after the assassination of Archduke Franz Ferdinand, which led to the war. The other Central Powers on the German side signed separate treaties. Although the armistice of 11 November 1918 ended the actual fighting, and agreed certain principles and conditions including the payment of reparations, it took six months of Allied negotiations at the Paris Peace Conference to conclude the peace treaty. Germany was not allowed to participate in the negotiations before signing the treaty.