What other material would you need to look / have access to in order to figure out what happened at the Homestead plant?

the Homestead Strike was a violent labour dispute between the Carnegie Steel Company and many of its workers that occurred in 1892 in Homestead, Pennsylvania. The striking workers were all fired on July 2, and on July 6 private security guards hired by the company arrived. The guards and workers exchanged gunfire, and at least three guards and seven workers were killed during the battle and its aftermath.

Explanation: GOOD LUCK

the crusaders are identified in the painting;

c. by the red crosses on their backs