How did the sinking of the Lusitania affect wartime propaganda? It proved that much anti-German propaganda was false. It provided new material for anti-German propaganda. It supported propaganda criticizing the Allied nations. It showed that propaganda against the Allies was false.

It provided new material for anti-German propaganda.

Explanation:

The attack of the luxury steamship Lusitania on 17th May 1915 killed more than a hundred of American people. Though owned by the British, the ship's passengers were mostly American nationals. And though running as a passenger ship, there was widespread rumor and understanding that the British government had prepared even their passenger ships as war vessels in case of emergencies. And it was also believed that weapons were being transported in such ships from the US to Europe.

With that knowledge in mind, the Germans began to deem any vessel plying around the British Isles a war zone. This led to the Lusitania being torpedoed which angered the United States, who up till now, had been a neutral country. But with this act, anti-German propaganda began to increase and led the US to take sides during the First World War.  

general allotment act (dawes act) february 8, 1887

amendment to the dawes act, february 28, 1891

commission to the five civilized tribes (dawes commission), march 3, 1893