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.

The treaty required Germany to disarm, make territorial concessions, extradite alleged war criminals, agree to Kaiser Wilhelm being put on trial, recognise the independence of states whose territory had previously been part of the German Empire, and pay reparations to the Entente powers. The most critical and controversial provision in the treaty was: "The Allied and Associated Governments affirm and Germany accepts the responsibility of Germany and her allies for causing all the loss and damage to which the Allied and Associated Governments and their nationals have been subjected as a consequence of the war imposed upon them by the aggression of Germany and her allies." The other members of the Central Powers signed treaties containing similar articles. This article, Article 231, became known as the "War Guilt" clause.

Many in China felt betrayed as the German territory in China was handed to Japan. Wellington Koo refused to sign the treaty and the Chinese delegation at the Paris Peace Conference was the only nation that did not sign the Treaty of Versailles at the signing ceremony. The sense of betrayal led to great demonstrations in China such as the May 4th movement. There was immense dissatisfaction with Duan Qirui's government, which had secretly negotiated with the Japanese in order to secure loans to fund their military campaigns against the south. On 12 June 1919, the Chinese cabinet was forced to resign and the government instructed its delegation at Versailles not to sign the treaty. As a result, relations with the Western world deteriorated.