
Background
- When war broke out in Europe in 1914, President Woodrow Wilson declared U.S. neutrality, reflecting both isolationist traditions and economic pragmatism.
- Yet, between 1914 and 1917, neutrality proved increasingly difficult to maintain. Economic interests, submarine warfare, and ideological factors gradually drew the U.S. into the First World War.
- The conflict marked a decisive moment: the United States emerged as a global power, while Wilson’s postwar vision tested the limits of American internationalism.
Neutrality and Early Involvement (1914–1916)
- The U.S. initially pursued a policy of neutrality, supplying both sides with goods while officially avoiding entanglement.
- American banks and industries soon became heavily invested in the Allied Powers, especially Britain and France, through loans and trade in weapons, food, and raw materials.
- The U.S. economy prospered, but neutrality increasingly tilted toward the Allies as British naval blockades restricted trade with Germany.
- Public opinion favored peace but was divided: many Americans of German and Irish descent opposed involvement, while others were swayed by reports of German aggression in Belgium and unrestricted submarine warfare.

The Lusitania Crisis (1915)
- On May 7, 1915, a German U-boat sank the British passenger liner RMS Lusitania, killing 1,198 people, including 128 Americans.
- Germany defended the attack by claiming the ship carried war supplies, but the incident shocked U.S. public opinion.
- Wilson demanded an end to unrestricted submarine warfare and warned that future violations would force the U.S. to act.
- Although war was still avoided, the event deepened the moral divide between neutrality and intervention, and U.S. preparedness efforts began to expand.
Unrestricted Submarine Warfare
A German naval strategy of sinking any vessel, including civilian ships, in war zones without warning.
Reasons for U.S. Entry into the War (1917)
- By 1917, neutrality was unsustainable. Germany resumed unrestricted submarine warfare, sinking American merchant ships.
- The Zimmermann Telegram (January 1917) was a secret German proposal offering Mexico U.S. territory in exchange for joining the war.
- Economic motives also played a role: protecting billions of dollars in U.S. loans and trade with the Allies became essential.
- Wilson framed intervention as a moral mission: to make the world “safe for democracy.”
- The U.S. formally declared war on Germany on April 6, 1917, entering the conflict as an Associated Power, not a formal ally, to preserve independence in policymaking.

Zimmermann Telegram
A secret German message proposing an alliance with Mexico against the U.S.; its interception by Britain inflamed American public opinion and hastened entry into the war.


