The Infantry in the American Civil War comprised foot-soldiers who fought primarily with small arms, and they carried the brunt of the fighting on battlefields across the United States. As the Civil War progressed, battlefield tactics soon changed in response to the new form of warfare being waged in America. The use of military balloons, rifled muskets, repeating rifles, and fortified entrenchments contributed to the death of many men. Generals and other officers, many professionally trained in tactics from the Napoleonic Wars, were often slow to develop changes in tactics in response.
Outbreak of war
At the start of the Civil War, the entire United States Army consisted of some 16,000 men of all branches, with infantry representing the vast majority of this total. Some of these infantrymen had seen considerable combat experience in the Mexican-American War, as well as in the West in various encounters, including the Utah War and several campaigns against Indians. However, the majority spent their time on garrison or fatigue duty. In general, the majority of the infantry officers were graduates of military schools such as the United States Military Academy.
In some cases, individual states, such as New York, had previously organized formal militia infantry regiments, originally to fight Indians in many cases, but by 1861, they existed mostly for social camaraderie and parades. These organizations were more prevalent in the South, where hundreds of small local militia companies existed.
With the secession of eleven Southern states by early 1861 following the election of President Abraham Lincoln, tens of thousands of Southern men flocked to hastily organized companies, which were soon formed into regiments, brigades, and small armies, forming the genesis of the Confederate States Army. Lincoln responded by issuing a call for 75,000 volunteers, and later even more, to put down the rebellion, and the Northern states responded. The resulting forces came to be known as the Volunteer Army (even though they were paid), versus the Regular Army. Infantry comprised over 80% of the manpower in these forces.
The typical infantry regiment of the early Civil War consisted of 10 companies (each with exactly 100 men, according to Hardee's 1855 manual, and led by a captain, with associated lieutenants). Field officers normally included a colonel (commanding), lieutenant colonel, and at least one major. With attrition from disease, battle casualties, and transfers, by the mid-war, most regiments averaged 300-400 men. Volunteer regiments were paid by the individual states, and officers at first were normally elected by popular vote, or were appointed by the state governors (particularly the colonels, who were often the men who had raised and organized the regiment). As the war progressed, the War Department and superior officers began selecting regimental leaders, and the regimental officers normally selected the NCOs (non-commissioned officers) based on performance and merit, although the individual states retained considerable influence in the selection of the regimental officers.
Often, and always, according to Hardee's 1855 manual, large regiments were broken into two or more battalions, with the lieutenant colonel and major(s) in charge of each battalion. The regiment may have also been divided into two wings, the left and right, for instructional purposes, only. The regimental commander exercised overall tactical control over these officers and usually relied on couriers and staff to deliver and receive messages and orders. Normally positioned in the center of the regiment in battle formation was the color guard, typically five to eight men assigned to carry and protect the regimental and/or national colors, led by a color sergeant. Most Union regiments carried both banners; the typical Confederate regiment simply had a national standard.
Individual regiments (usually three to five, although the number varied) were organized and grouped into a larger body (a brigade) which soon became the main structure for battlefield maneuvers. Generally, the brigade was commanded by a brigadier general or senior colonel, when merit was clearly evident in that colonel and a Brigadier was not available. Two to four brigades typically comprised a division, which in theory was commanded by a major general, but theory was often not put into practical application, especially when an officer exhibited exceptional merit or the division was smaller and trusted to a more junior officer. Several divisions would constitute a corps, and multiple corps together made up an army, often commanded by a lieutenant general or full general in the Confederate forces, and by a major general in the Union forces.