When World War I began in August 1914, many people anticipated that the war would end by Christmas of that year. Which event extended the war into 1915 and beyond?

The German army advanced through Belgium toward Paris, hoping to defeat France quickly. In September 1914, French forces and their British allies stopped the German advance at the First Battle of the Marne, preventing a swift victory and helping turn the western front into a prolonged stalemate. The Americans did not enter the war until 1917, and the Russian Revolution occurred later, in 1917.

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