In 1917, two significant events changed the course of the war.
German U-Boats kept attacking unarmed passenger and merchant ships. In 1915, they torpedoed the British ocean liner ‘The Lusitania’. It sank immediately and 1,200 people lost their lives, among them 128 Americans. This led to massive anti-German sentiment in the United States. Two years later, a letter was intercepted, showing that the Germans tried to make an alliance with Mexico to attack the United States. On 6th April 1917, the United States Congress voted to join the Allies in the war.