The initial war fever soon dissipated in both the North and South, and each side was compelled to resort to conscription. The South instituted a draft in 1862, requiring three years of service for those selected between the ages of 18 and 35; later, as the war prospects dimmed, the pool was enlarged by taking in ages 17 to 50. A large number of exemptions were allowed and there were provisions for substitutions.

The threat of a draft was used in Missouri and Iowa to speed up the rate of volunteer enlistment. The Militia Act of 1862 gave the President authority to draft 300,000 militiamen for up to nine months. It was to be a state run affair, with each county to be involved in the selection. However, the threat of conscription was for the time being enough to keep enlistments at an adequate level.
The Draft Act of 1863 was the first instance of compulsory service in the federal military services. All male citizens, as well as aliens who had declared their intention of becoming citizens, between 20 and 45 were at risk of being drafted. No married man could be drafted until all the unmarried had been taken.

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