The Paris Peace Conference was the formal meeting in 1919 and 1920 of the victorious Allies after the end of World War I to set the peace terms for the defeated Central Powers. Dominated by the leaders of Britain, France, the United States and Italy, it resulted in five treaties that rearranged the maps of Europe and parts of Asia, Africa and the Pacific Islands, and also imposed financial penalties. Germany and the other losing nations had no voice in the Conference's deliberations; this gave rise to political resentments that lasted for decades.

The conference involved diplomats from 32 countries and nationalities. Its major decisions were the creation of the League of Nations and the five peace treaties with the defeated states; the awarding of German and Ottoman overseas possessions as "mandates", chiefly to Britain and France; the imposition of reparations upon Germany; and the drawing of new national boundaries, sometimes involving plebiscites, to reflect ethnic boundaries more closely.

Wilson's liberal internationalist foreign policy goals, stated in the Fourteen Points, became the basis for the terms of the German surrender during the conference, as it had earlier been the basis of the German governments negotiations in the Armistice of 11 November 1918.

The main result was the Treaty of Versailles with Germany; Article 231 of the treaty placed the whole guilt for the war on "the aggression of Germany and her allies". That provision proved very humiliating for Germany, and set the stage for the expensive reparations that Germany was intended to pay (it paid only a small portion before its last payment in 1931). The five great powers (France, Britain, Italy, Japan and the United States) controlled the Conference. The "Big Four" were French Prime Minister Georges Clemenceau, British Prime Minister David Lloyd George, US President Woodrow Wilson, and Italian Prime Minister Vittorio Emanuele Orlando. They met informally 145 times and made all major decisions before they were ratified.The conference began on 18 January 1919. With respect to its end, Professor Michael Neiberg noted, "Although the senior statesmen stopped working personally on the conference in June 1919, the formal peace process did not really end until July 1923, when the Treaty of Lausanne was signed."It is often referred to as the "Versailles Conference", but only the signing of the first treaty took place there, in the historic palace; the negotiations occurred at the Quai d'Orsay, in Paris.

World War I, often abbreviated as WWI or WW1, also known as the First World War and contemporaneously known as the Great War and by other names, was an international conflict that began on 28 July 1914 and ended on 11 November 1918. It involved much of Europe, as well as Russia, the United States and Turkey, and was also fought in the Middle East, Africa and parts of Asia. One of the deadliest conflicts in history, an estimated 9 million were killed in combat, while over 5 million civilians died from occupation, bombardment, hunger or disease. The genocides perpetrated by the Ottomans and the 1918 Spanish flu pandemic spread by the movement of combatants during the war caused many millions of additional deaths worldwide.In 1914, the Great Powers were divided into two opposing alliances: the Triple Entente, consisting of France, Russia, and Britain, and the Triple Alliance, made up of Germany, Austria-Hungary, and Italy. Tensions in the Balkans came to a head on 28 June 1914 following the assassination of Archduke Franz Ferdinand, the Austro-Hungarian heir, by Gavrilo Princip, a Bosnian Serb. Austria-Hungary blamed Serbia and the interlocking alliances involved the Powers in a series of diplomatic exchanges known as the July Crisis. On 28 July, Austria-Hungary declared war on Serbia; Russia came to Serbia's defence and by 4 August, the conflict had expanded to include Germany, France and Britain, along with their respective colonial empires. In November, the Ottoman Empire, Germany and Austria formed the Central Powers, while in April 1915, Italy joined Britain, France, Russia and Serbia as the Allied Powers.

Facing a war on two fronts, German strategy in 1914 was to defeat France, then shift its forces to the East and knock out Russia, commonly known as the Schlieffen Plan. This failed when their advance into France was halted at the Marne; by the end of 1914, the two sides faced each other along the Western Front, a continuous series of trench lines stretching from the Channel to Switzerland that changed little until 1917. By contrast, the Eastern Front was far more fluid, with Austria-Hungary and Russia gaining, then losing large swathes of territory. Other significant theatres included the Middle East, the Alpine Front and the Balkans, bringing Bulgaria, Romania and Greece into the war.

Shortages caused by the Allied naval blockade led Germany to initiate unrestricted submarine warfare in early 1917, bringing the previously neutral United States into the war on 6 April 1917. In Russia, the Bolsheviks seized power in the 1917 October Revolution and made peace in the March 1918 Treaty of Brest-Litovsk, freeing up large numbers of German troops. By transferring these to the Western Front, the German General Staff hoped to win a decisive victory before American reinforcements could impact the war, and launched the March 1918 German spring offensive. Despite initial success, it was soon halted by heavy casualties and ferocious defence; in August, the Allies launched the Hundred Days Offensive and although the German army continued to fight hard, it could no longer halt their advance.Towards the end of 1918, the Central Powers began to collapse; Bulgaria signed an Armistice on 29 September, followed by the Ottomans on 31 October, then Austria-Hungary on 3 November. Isolated, facing revolution at home and an army on the verge of mutiny, Kaiser Wilhelm abdicated on 9 November and the new German government signed the Armistice of 11 November 1918, bringing the fighting to a close. The 1919 Paris Peace Conference imposed various settlements on the defeated powers, the best known being the Treaty of Versailles. The dissolution of the Russian, German, Ottoman and Austro-Hungarian empires led to numerous uprisings and the creation of independent states, including Poland, Czechoslovakia and Yugoslavia. For reasons that are still debated, failure to manage the instability that resulted from this upheaval during the interwar period ended with the outbreak of World War II in 1939.