World War 1 introduced the world to trench warfare and lethal new weapons such as poison gas. The war also reshaped the map of Europe, eliminating the sprawling Austro-Hungarian, Ottoman and Russian empires and creating new ones to take their place. It would kill over 16 million military personnel and an unknown number of civilians and would spark political turmoil that contributed to a second, bloodier world war two decades later.

The outbreak of World War 1 was triggered by many factors, including a growing rivalry between Germany and Britain for control over European colonial possessions; the rise of nationalism in which people decided their loyalty based on ethnic or cultural origin; and German militarism, which provoked attacks by Austria-Hungary, Italy and Japan. It also reflected a time when governments engaged in “secret diplomacy” to try to outmaneuver their opponents, sometimes engaging in actions that were illegal under international law.

When the war ended in 1918, more than four million Americans had served in the armed forces and more than 116,708 had died. The resulting Allied victory altered the world forever, ushering in the era of the United Nations and other global institutions to protect future generations from the scourge of war. It also shaped the writings of Ernest Hemingway and John Dos Passos and helped shape the careers of military leaders such as Dwight D. Eisenhower, George S. Patton and George C. Marshall.