Reasons America Declared War On Germany In the years leading up to 1917, a multitude of reasons contributed to the American decision to declare war on Germany. These reasons include the German naval policy, allied propaganda, and America’s claim to world power. The German U-boats as well as the incident with the Lusitania prompted America to take action. Propaganda, exaggerated or not, helped to get the people’s support for declaring war. Lastly, America believed that by partaking in the war would increase its chances of getting concessions at the end of the war, thereby supporting its claim to worl