Final answer:
Lincoln's initial call for troops in 1861 aimed to suppress the Southern rebellion and preserve the Union, with emancipation becoming a main objective later on during the Civil War.
Step-by-step explanation:
President Abraham Lincoln called for volunteers to join the U.S. military in 1861 with the primary goal of preserving the Union by putting down the Southern rebellion. Although Lincoln eventually embraced emancipation as a military necessity to undermine the Confederacy's capacity for war, his initial call to arms in April 1861, after the fall of Fort Sumter, was focused on quickly suppressing the Confederate uprising and eliminating the threat of secession, rather than on ending slavery. The hope was that a swift show of force would bring the seceding states back into the Union and restore national unity. The question of slavery, though deeply intertwined with the conflict, became more central to the Union's war aims with the issuance of the Emancipation Proclamation in 1863, which also allowed for the recruitment of African American soldiers.