American Military History, Volume 1 by Richard W. Stewart

As North and South lined up for battle, the preponderance of productive capacity, manpower, and agricultural potential clearly lay on the side of the North. Its crops were worth more annually than those of the South, which had concentrated on growing cotton, tobacco, and rice. Between February and May 1861 the Confederate authorities missed the opportunity to ship baled cotton to England and draw bills against it for the purchase of arms. In sea power, railroads, material wealth, and industrial capacity to produce iron and munitions, the North was vastly superior to the South. This disparity became even more pronounced as the ever-tightening blockade gradually cut off the Confederacy from foreign imports. The North had more mules and horses, a logistical advantage of great importance since supplies had to be carried to the troops from rail and riverheads.

The difference in manpower was also critical. According to the census of 1860, the population of the United States numbered 31,443,321. About 23 million of them were in the twenty-two Northern states and 9 million in the eleven states that later seceded. Of the latter total, 3.5 million were slaves. The size of the opposing armies would reflect this disparity. At one time or another about 2.1 million men would serve in the Northern armies, while 800,000–900,000 men would serve the South. Peak strength of the two forces would be about 1 million and 600,000, respectively.