When World War I broke out in Europe in 1914, President Woodrow Wilson declared the United States neutral. This continued the government’s 19^th century policy of isolationism – staying out of the affairs of other countries. There were mixed sympathies for both Allied and Central Power efforts as nearly 2/3 of Americans had either direct or immigrant heritage to the people groups drawn into this devastating conflict. However, most Americans had no desire to enter the war.

The U.S. was undergoing tremendous economic, agricultural and industrial growth – and facing major social change. Public focus primarily remained on domestic issues; American sentiments were gradually influenced by unfolding events in Europe. Stories of German brutality, particularly the invasion of neutral Belgium, and personal accounts of the German policy of unrestricted submarine warfare began to sway public opinion in the United States against Germany. The most prominent example was the sinking of the passenger liner Lusitania, which was carrying ammunition exports, in May 1915 when 128 Americans of nearly 1200 civilians onboard died. By 1916 a Preparedness Movement arose that argued for a military build-up and even entry into the “Great War.” However, there was no widespread support to join the war. Advocates of peace argued for the continuation of American neutrality, a position reflected in Woodrow Wilson’s winning slogan in the 1916 presidential election, “He Kept Us Out of War.”

In early 1917, a series of events finally drew the U.S. into the war. On Feb. 1, Germany took a calculated risk to resume unrestricted submarine warfare to try to topple the British naval blockade of both Germany military and civilian supplies. The U.S. responded by breaking all diplomatic relations with Germany. Later that month, British diplomats shared a decoded telegram from Germany’s Foreign Minister Arthur Zimmermann to the German ambassador in Mexico. The message promised to help Mexico recapture territory lost to the U.S. during the Mexican American War (1846–1848) if Mexico allied with Germany. The Zimmermann Telegram, as it came to be called, was published in American newspapers on March 1, further fueling anti-German sentiment that finally came to a tipping point by the end of the month, by which point German submarines had sunk five U.S. merchant ships, killing dozens of Americans onboard. On April 2, President Wilson delivered a war message to Congress, asking it to declare war on Germany. The Senate granted Wilson’s request two days later, followed by the House of Representatives on April 6. The United States had officially entered World War I.