May Fourth Movement: Student demonstrations take place in Tiananmen Square in Beijing, China, protesting the Treaty of Versailles, which transferred Chinese territory to Japan.

The Treaty of Versailles (French: Trait de Versailles; German: Versailler Vertrag, pronounced [vza ftak] (listen)) was the most important of the peace treaties of World War I. It ended the state of war between Germany and the Allied Powers. It was signed on 28 June 1919 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, it took six months of Allied negotiations at the Paris Peace Conference to conclude the peace treaty. The treaty was registered by the Secretariat of the League of Nations on 21 October 1919.

Of the many provisions in the treaty, one of the most important and controversial 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. The treaty required Germany to disarm, make ample territorial concessions, and pay reparations to certain countries that had formed the Entente powers. In 1921 the total cost of these reparations was assessed at 132 billion gold marks (then $31.4 billion or £6.6 billion, roughly equivalent to US$442 billion or UK£284 billion in 2022).

Prominent economists such as John Maynard Keynes declared the treaty too harsha "Carthaginian peace"and said the reparations were excessive and counter-productive. On the other hand, prominent Allied figures such as French Marshal Ferdinand Foch, criticized the treaty for treating Germany too leniently. This is still the subject of ongoing debate by historians and economists.

The result of these competing and sometimes conflicting goals among the victors was a compromise that left no one satisfied. In particular, Germany was neither pacified nor conciliated, nor was it permanently weakened. The problems that arose from the treaty would lead to the Locarno Treaties, which improved relations between Germany and the other European powers, and the re-negotiation of the reparation system resulting in the Dawes Plan, the Young Plan, and the indefinite postponement of reparations at the Lausanne Conference of 1932. The treaty has sometimes been cited as a cause of World War II: although its actual impact was not as severe as feared, its terms led to great resentment in Germany which powered the rise of the Nazi Party.

Although it is often referred to as the "Versailles Conference", only the actual signing of the treaty took place at the historic palace. Most of the negotiations were in Paris, with the "Big Four" meetings taking place generally at the French Ministry of Foreign Affairs on the Quai d'Orsay.

The May Fourth Movement was a Chinese anti-imperialist, cultural, and political movement which grew out of student protests in Beijing on May 4, 1919. Students gathered in front of Tiananmen (The Gate of Heavenly Peace) to protest the Chinese government's weak response to the Treaty of Versailles decision to allow Japan to retain territories in Shandong that had been surrendered to Germany after the Siege of Tsingtao in 1914. The demonstrations sparked nation-wide protests and spurred an upsurge in Chinese nationalism, a shift towards political mobilization away from cultural activities, a move towards a populist base and away from traditional intellectual and political elites.

The May Fourth demonstrations marked a turning point in a broader anti-traditional New Culture Movement (1915–1921) that sought to replace traditional Confucian values and was itself a continuation of late Qing reforms. Yet even after 1919, these educated "new youths" still defined their role with a traditional model in which the educated elite took responsibility for both cultural and political affairs. They opposed traditional culture but looked abroad for cosmopolitan inspiration in the name of nationalism and were an overwhelmingly urban movement that espoused populism in an overwhelmingly rural country. Many political, and social leaders of the next five decades emerged at this time, including those of the Chinese Communist Party.