From the closing days of the Revolutionary War in 1783 to the beginning of the War of 1812, the United States Army faced one of its most challenging periods. During this era, American soldiers confronted threats from Great Britain, France, and Spain. On the western frontier, hostile warriors from American Indian nations battled U.S. Army and militia troops north of the Ohio River, as white settlers' insatiable demands for land provoked conflict with Indian communities. The Army suppressed civil unrest, built roads, and conducted explorations, including the transcontinental expedition led by Army officers Meriwether Lewis and William Clark. The post-revolutionary years also saw the Army in a process of frequent reorganization, from the disbanding of the Continental Army at the end of the Revolutionary War to the establishment of Maj. Gen. Anthony Wayne's Legion of the United States, followed by President Thomas Jefferson's efforts at reforming the Army into a Republican institution. These structural changes increased during James Madison's first presidential term, as Americans prepared for war with Great Britain over maritime rights, free trade, and territorial expansion in a conflict that became known as the War of 1812. Illustrated with photographs, artwork and maps, this explains how the United States' Army was transformed in its first four decades.