Final answer:
The AEF led by General John J. Pershing made significant contributions, including the introduction of new weapons technology and key victories in battles, which helped turn the tide of World War I.
Step-by-step explanation:
The American Expeditionary Force (AEF) led by General John J. Pershing made significant contributions during World War I. One of the main contributions was the introduction of new weapons technology, such as tanks and machine guns, which helped turn the tide of the war in favor of the Allies. The AEF also played a crucial role in stopping the German advance in key battles like Cantigny, Chateau-Thierry, Belleau Wood, Second Battle of Marne, Saint-Mihiel, and Meuse-Argonne. These victories helped weaken the German army and ultimately led to the end of the war.