Answer:
The U.S. Army was little more than a militia at the time.
Explanation:
The U.S. Army had only been founded 90 years prior to the end of the war. In that time, the only recognized conflict was the War of 1812. The Union did not have a lot of time to mobilize, as well as the problem of men not wanting to leave their homes. The Confederacy had slaves to tend their farms and had the advantage of mobilizing quicker than the Union Army.
