Final answer:
President Lincoln's military experience at the outbreak of war was limited to his time as a captain in the Illinois militia during the Black Hawk War, lacking formal military training or experience to inform his Civil War decision-making.
Step-by-step explanation:
The best description of President Abraham Lincoln's military experience at the outbreak of the Civil War is that he had limited military experience. Lincoln did not have extensive formal military training, nor did he serve as a general in the Union Army, and he certainly never led the Confederate Army. His involvement in the Black Hawk War of 1832 as a captain in the Illinois militia represents the extent of his military experience before becoming President and facing the complex military challenges of the Civil War.
As President, Lincoln had to navigate the political landscape and make strategic military decisions without the benefit of a formal military education or extensive firsthand experience. His role was to shape the overall strategy to preserve the Union, which included calling for volunteers, establishing a naval blockade, and dealing with the issue of slavery as it pertained to the war effort.