The Regular Army of the United States was and is the successor to the Continental Army as the country's permanent, professional military establishment. Even 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, the small Regular Army of the United States was supported by State militias and volunteer regiments organized by States but thereafter controlled by federal authorities and generals in time of war. 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. In contemporary use, the term Regular