As the American Revolutionary War unfolded in North America, there were two principal campaign theaters within the thirteen states, and a smaller but strategically important one west of the Appalachian Mountains to the Mississippi River and north to the Great Lakes. The full-on military campaigning began in the states north of Maryland, and fighting was most frequent and severest there between 1775 and 1778. Patriots achieved several strategic victories in the South, the British lost their first army at Saratoga, and the French entered the war as an American ally.