In the late 19th century, three brilliant inventors, Thomas Edison, Nikola Tesla and George Westinghouse, battled over which electricity system—direct current (DC) or alternating current (AC)–would become standard. During their bitter dispute, dubbed the War of the Currents, Edison championed the direct-current system, in which electrical current flows steadily in one direction, while Tesla and Westinghouse promoted the alternating-current system, in which the current’s flow constantly alternates.

The most famous of the three visionary men, Edison, developed the world’s first practical light bulb in the late 1870s, then began building a system for producing and distributing electricity so businesses and homes could use his new invention. He opened his first power plant, in New York City, in 1882. Two years later, Tesla, a young Serbian engineer, immigrated to America and went to work for Edison. Tesla helped improve Edison’s DC generators while also attempting to interest his boss in an AC motor he’d been developing; however, the Wizard of Menlo Park, a firm supporter of DC, claimed AC had no future. Tesla quit his job in 1885 and a few years later received a number of patents for his AC technology. In 1888, he sold his patents to industrialist George Westinghouse, whose Westinghouse Electric Company had quickly become an Edison competitor.

Feeling threatened by the rise of AC, which could be distributed over long distances much more economically than DC, Edison launched a propaganda campaign to discredit AC and convince the public it was dangerous. As part of this campaign, animals were publicly electrocuted with AC, and when New York State sought a more humane alternative to hanging its death-penalty prisoners, Edison, once an opponent of capital punishment, recommended alternating current-powered electrocution as the fastest, deadliest option. In 1890, convicted murderer William Kemmler became the first person to die in the electric chair. The apparatus, designed by an electricity salesman secretly on Edison’s payroll, was powered by a Westinghouse AC generator.

Ultimately, however, Edison failed in his efforts to discredit AC. Westinghouse won the contract to supply electricity to the 1893 World’s Fair in Chicago—beating out rival General Electric, which was formed in 1892 by a merger involving Edison’s company—and the expo became a dazzling showcase for Tesla’s AC system. Westinghouse also received an important contract to construct the AC generators for a hydro-electric power plant at Niagara Falls; in 1896, the plant started delivering electricity all the way to Buffalo, New York, 26 miles away. The achievement was regarded as the unofficial end to the War of the Currents, and AC became dominant in the electric power industry.