By April 1861 it had become clear that war was inevitable. On April 16 Steuart's eldest son, George H. Steuart, then an officer in the United States Army, resigned his captain's commission to join the Confederacy. On April 19 Baltimore was disrupted by riots, during which Southern sympathizers attacked Union troops passing through the city by rail, causing what were arguably the first casualties of the Civil War. Steuart ordered his militia to assemble, armed and uniformed, to repel the Federal soldiers, as Steuart himself was strongly sympathetic to the Confederacy, along with most of his senior officers. It is possible that he may even have contemplated an invasion of Washington DC. Perhaps knowing this, and no doubt aware that public opinion in Baltimore was divided, Governor Thomas Holliday Hicks refused to order out the militia. Steuart's eldest son commanded one of the city militias during the disturbances of April 1861 and, in a letter to his father, the younger Steuart wrote: