Summarize why 1917 is a turning point in World War 1.

The entry into the war of the USA with its enormous resources in spring 1917 led to the conflict taking a clear and critical turn in favor of the Western Powers. The decision of the German high command to pursue the war at sea was also a demonstration of Emperor Karl's powerlessness. 1917 saw the entry of America into World War One, the result of Germany's use of unrestricted submarine warfare. 1917 also saw the start of the Battle of Passchendaele, also known as the Third Battle of Ypres.