History of Warfare Summary 9 - World War I 13: US Entry into the War

Although the United States initially declared neutrality at the start of the war, it grew economically closer to the Allied powers by providing vast amounts of supplies and funds to Britain and France. Germany's submarine warfare escalated tensions with the U.S. The sinking of the British passenger liner Lusitania by a German submarine in 1915, in particular, intensified criticism against Germany within the United States. Germany temporarily refrained from unrestricted submarine warfare but resumed it in 1917. In the same year, the Zimmermann Telegram, which revealed Germany's proposal to Mexico for an alliance against the U.S., significantly swayed American public opinion. Consequently, the U.S. declared war on Germany in April 1917. While the American military did not immediately decide the war's outcome, its immense industrial capacity, manpower, and financial support became a crucial asset to the Allies. Especially as American Expeditionary Forces began arriving in Europe, Germany found it increasingly difficult to sustain its manpower and resource disadvantage in the long run. The U.S. entry into the war marked a significant turning point, shifting the balance of power in World War I.