The Union's response to the attack on Fort Sumter was a call for volunteers.

Following the attack on Fort Sumter on April 12, 1861, the Union made a call for military volunteers. President Abraham Lincoln requested 75,000 individuals to enlist for a three-month term, intending to suppress the rebellion and reestablish order. This mobilization represented a crucial turning point, energizing public support for the Union's efforts and resulting in a significant increase in enlistments. The response underscored the urgency and gravity of the situation, as the Union aimed to assert its determination against the Confederacy. This appeal for volunteers ultimately laid the groundwork for a lengthy and brutal conflict.