When these seven states seceded, it caused a breakup in the U.S. Army. Many were from the South and felt they had a responsibility to resign from the U.S. Army and join the Confederate Army. In April of 1861, the United States Army had only 16,000 men organized into fewer than 200 companies. Most of them were at posts west of the Mississippi River. While the army was made up of trained professional soldiers, Lincoln realized he could not put down a rebellion of this size with the army he had.