John Sherman of Ohio had served just five days as a United States senator when the Senate adjourned its special session on March 28, 1861. With Southern senators withdrawing as states seceded, and with all efforts at compromise apparently exhausted, a civil war seemed imminent. Fifteen days later, when shots were fired on Fort Sumter in Charleston Harbor, Sherman wrote to his brother William Tecumseh Sherman, "Civil War is actually upon us, and, strange to say, it brings a feeling of relief; the suspense is over."

While serving as a member of the House of Representatives, Sherman had been a favored Republican candidate for Speaker of the House before the Ohio legislature elected him to fill a Senate vacancy. Among those considered for the Senate seat was Ohio governor William Dennison.

Following the attack on Fort Sumter, President Lincoln issued a proclamation on April 15, 1861, summoning Congress to return for an extraordinary session on July 4, and calling forth the state militias. Anxious to assist in the war effort until Congress reconvened, Sherman offered his services to Governor Dennison in this letter dated April 20. "I wish no pay or emolument and still hope you may assign me some such position as I indicate," Sherman wrote. "If you do it I will obey your orders if you do not I will go to Phil[adelphia] or Washington."

Sherman ultimately found work as an aide de camp to General Robert Patterson until the Senate session began. He also raised a brigade of Ohioans which became known as Sherman's Brigade.