the term of service differed. In April, 1861 President Lincoln called for 75,000 militia for 3 months. This was followed by various calls on the States for volunteers...
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The Confederacy first established the Provisional Army of the Confederate States in March, 1861, and the States contributed their State troops to it. The CSA also raised large numbers of volunteers. These were mostly for one year.
In 1862 with the reorganization of the army, all units were to serve three years or the war, etc.