The First Battle of the Marne, fought from September 6 to September 12, 1914, was a pivotal conflict during World War I where Allied forces halted the German advance into France. This battle marked a significant turning point, leading to the establishment of trench warfare on the Western Front and changing the course of the war. Its outcome played a crucial role in undermining German plans for a quick victory and began a prolonged stalemate that would define much of the war.