America's Role in the World: World War I to World War II

Between World War I and World War II the United States emerged on the world stage as a superpower. This ascendancy had military, economic, humanitarian, and cultural dimensions. Some Americans expressed discomfort with this unwelcome new role, believing that it ran counter to the nation’s traditions of isolation from Europe’s internecine wars. Others argued that in an interconnected and global world order, the days of isolation and neutrality were long over. Still others saw an opportunity to remake the world in America’s image, promoting democracy and free markets as a means of ensuring world prosperity and peace.

Although few Americans in 1914 wanted to enter World War I, the majority believed that the United States had an obligation to ensure that autocratic Germany did not destroy the democracies of France and Great Britain. Millions of Americans gave of their time and their money to help the Allied cause. Tens of thousands volunteered as doctors, nurses, ambulance drivers, airmen, and soldiers in the British and French armies. The sinking of the Lusitania in 1915 proved to Americans that they would not be able to remain neutral merely because they wanted to. The war was coming ever closer to American shores.

In April 1917 the United States finally felt a sufficient threat to enter the war. The Germans had resumed unrestricted submarine warfare and, through the Zimmerman Telegram, had proposed the creation of a German-Mexican-Japanese alliance aimed at dividing the American West between them. President Wilson pledged to seek no territorial expansion through foreign war, a first in American history. He spoke in idealistic terms about American war aims in his famous Fourteen Points speech of January 1918.

Despite the victory on the battlefield, many Americans grew despondent and disillusioned by the failures of the Paris Peace Conference. The war had not, in the end, made the world any safer or more democratic. The United States remained active in international affairs in the 1920s and 1930s, but the American people and their leaders remained wary of fighting another war.

The fall of France in 1940 shook Americans out of their slumber. They responded with massive defense spending bills and an unprecedented introduction of conscription in peacetime. Isolationism faded but did not entirely vanish until the Japanese attack on Pearl Harbor of December 7, 1941.

The Second World War made the United States a true superpower with atomic weapons and a booming economy. American losses in material and human costs had been far lower than those of China, the Soviet Union, or Germany, leaving the nation in a position of dominance. Still, Americans debated whether to use that power or retreat into isolation once more. Even before the war ended, however, the United States made its choice to be a more active player in the world, helping to usher in the United Nations and creating the Bretton Woods economic system. Questions remained, however, about the proper place of the United States in the world, questions that stay with us even today.

Michael Neiberg is the chair of War Studies at the US Army War College and the author of Potsdam: The End of World War II and the Remaking of Europe (2015) and Dance of the Furies: Europe and the Outbreak of War, 1914 (2011).