Final answer:
The defeat of German forces by half a million soldiers at Saint-Mihiel occurred in September 1918. This was a key victory for the American Expeditionary Forces and paved the way for the Meuse-Argonne offensive, contributing to the end of World War I.
Step-by-step explanation:
The battle where half a million soldiers defeated the Germans at Saint-Mihiel took place in September 1918. It was part of a series of offensives by the American Expeditionary Forces (AEF) along with French support which aimed to reduce the Saint-Mihiel salient.
The AEF and its allies managed to push back the German forces, and this victory was significant in the overall course of World War I. In the later stages of the conflict, particularly in November 1918, the German military command acknowledged the desperate situation and advised Emperor Kaiser Wilhelm II to seek peace negotiations. The ceasefire and armistice were declared on November 11, 1918, bringing the fighting to a halt.
The victory at Saint-Mihiel helped prepare the AEF for their role in the Meuse-Argonne offensive, a major part of the final Allied offensives which contributed to the end of the war. The successful operations by the United States and Allied forces during this period marked a turning point against the Central Powers, leading to the eventual withdrawal of Germany and the cessation of World War I.