The event in 1917 that most benefited the Allies was the United States declaring war against Germany.
The event in 1917 that most benefited the Allies was the United States declaring war against Germany. To get the answer, you can look at the historical context of World War I. In 1917, the Allies (which included countries such as the United Kingdom, France, and Russia) were locked in a stalemate with the Central Powers (Germany, Austria-Hungary, and the Ottoman Empire). The entry of the United States into the war provided a significant boost to the Allies' resources, manpower, and military capabilities, ultimately tipping the balance in their favor. With the United States joining the war effort, the Allies gained a powerful ally and additional resources, allowing them to mount a more effective offensive against the Central Powers.
