In 1887 direct current (DC) was king. At that time there were 121 Edison power stations scattered across the United States delivering DC electricity to its customers. But DC had a great limitation — namely, that power plants could only send DC electricity about a mile before the electricity began to lose power. So when George Westinghouse introduced his system based on high-voltage alternating current (AC), which could carry electricity hundreds of miles with little loss of power, people naturally took notice. A “battle of the currents” ensued. In the end, Westinghouse’s AC prevailed.
Source: PBS