World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a global conflict between two coalitions: the Allies (or Entente) and the Central Powers. Main areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. In Europe, the stalemate caused by trench warfare led to technological innovations such as tanks and aircraft, along with the widespread use of artillery, machine guns, and chemical weapons. One of the deadliest conflicts in history, it resulted in an estimated 30 million military casualties, plus another 8 million civilian deaths from war-related causes and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic.

The causes of World War I included the rise of Germany and decline of the Ottoman Empire, which disturbed the long-standing balance of power in Europe, and rising economic competition between nations driven by industrialisation and imperialism. Growing tensions between the great powers and in the Balkans reached a breaking point on 28 June 1914, when Gavrilo Princip, a Bosnian Serb, assassinated the heir to the Austro-Hungarian throne. Austria-Hungary blamed Serbia, and declared war on 28 July. After Russia mobilised in Serbia's defence, Germany declared war on Russia and France, who had an alliance. The United Kingdom entered after Germany invaded Belgium, and the Ottomans joined the Central Powers in November.

Thomas Woodrow Wilson (December 28, 1856 – February 3, 1924) was the 28th president of the United States, serving from 1913 to 1921. He was the only Democrat to serve as president during the Progressive Era when Republicans dominated the presidency and legislative branches. As president, Wilson changed the nation's economic policies and led the United States into World War I. He was the leading architect of the League of Nations, and his stance on foreign policy came to be known as Wilsonianism.

Born in Staunton, Virginia, Wilson grew up in the Southern United States during the American Civil War and Reconstruction era. After earning a Ph.D. in history and political science from Johns Hopkins University, Wilson taught at several colleges prior to being appointed president of Princeton University, where he emerged as a prominent spokesman for progressivism in higher education. Wilson served as the governor of New Jersey from 1911 to 1913, during which he broke with party bosses and won the passage of several progressive reforms.

In the 1912 election, Wilson defeated incumbent Republican William Howard Taft and third-party nominee Theodore Roosevelt, becoming the first Southerner to win the presidency since the 1848 election. During his first year as president, Wilson authorized the widespread imposition of segregation inside the federal bureaucracy and his opposition to women's suffrage drew protests. His first term was largely devoted to pursuing passage of his progressive New Freedom domestic agenda. His first major priority was the Revenue Act of 1913, which began the modern income tax, and the Federal Reserve Act, which created the Federal Reserve System.

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.

Critics including John Maynard Keynes declared the treaty too harsh, styling it as a "Carthaginian peace", and saying the reparations were excessive and counterproductive.