The First American Regiment was the first peacetime regular army infantry unit authorized by the Confederation Congress after the American Revolutionary War. Organized in August 1784, it served primarily on the early American frontier west of the Appalachian Mountains. In 1815, following the end of the War of 1812, it was consolidated with several other regiments to form the 3rd Infantry Regiment.

The Regular Army of the United States succeeded the Continental Army as the country's permanent, professional land-based military force. In modern times, the professional core of the United States Army continues to be called the Regular Army. From the time of the American Revolution until after the Spanish–American War, state militias and volunteer regiments organized by the states supported the smaller Regular Army of the United States. These volunteer regiments came to be called United States Volunteers (USV) in contrast to the Regular United States Army (USA). During the American Civil War, about 97 percent of the Union Army was United States Volunteers.