The Central Powers (Austria, Germany, and Turkey) had been knocking the Allied Powers out of the war, including Italy and Russia.
The US came into the war as a result of Germany's declaration of war and initiation of unrestricted submarine warfare against US shipping in 1917.
The US built a large, new army just for the purpose of fighting in Europe, the AEF (American Expeditionary Force). It arrived and was in place just in time for the German Spring 1918 Offensive in France which almost knocked Britain and France out of the war.
The German army collided with the US Army (1st Marine Division made first contact) at the 2nd Battle of the Marne. The US won a decisive victory, driving the Germans back from Paris. The German army was on the defensive for the remainder of the war, and the US army played major roles in most of the subsequent Allied victories.
In summary, the arrived with a large, fresh army at the decisive time to turn the tide from Allied defeat into victory.
The Russian Revolution did not play a large part in the US government's decision to enter the War. The sinking of the Lusitannia, the Zimmerman Telegraph, unrestricted submarine warfare and propaganda played a much larger role in the decision.
Lincoln often communicated with his generals via telegraphs. It was the latest and fastest way to communicate ideas and plans to those out on the battlefield
The US provided millions of dollars in weapons, armament as well as money itself to the Allied forces. Victim, combatatant and victor, it was also called the "Arsenal of Democracy" and the "Breadbasket of the World."
Women began playing a large role in the workforce.
eugene debs
around 1950
It was the only role. Otherwise the US would have stayed out of it.
The role of Mobile, Alabama was a significant role in the US Civil War. The city passed several resolutions even passed a resolution to succeed from the Union.
He was a General of the US Armies
World War I
World War I
World War I
THE WAR? I think there has been more than one war
John Smith is a common US name; he was a US Serviceman.
It was a decisive US victory. See related questions for further details.
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The role of Pearl Harbor was US entry into WW2; making WW2 a truly Global War.