Thomas Alva Edison and Nicola Tesla should have been great friends, were it not for Edison being completely dedicated to DC electricity, and Tesla being completely dedicated to AC electricity. One can only imagine the progress that would have been made had the two gentlemen worked together.
Commercially, both men were in competition in the 1880s with world-wide electricity distribution rights at stake. New York City engaged Edison to begin lighting the city with his new electric street lights (which according to some sources of the day would only work on a DC supply, which is completely false, of course. This comment has been attributed to Edison, but also Joseph Swann).
Edison favoured local generation at a relatively low voltage, for one simple reason: DC won’t transform into higher or lower voltages, at least not before the invention of switch mode power supplies. The only way Edison could step-up, or step-down voltage was to run a DC generator off a DC motor. Low voltages lost too much energy over long distribution lines, due to low voltages to begin with, and high currents on the transmission lines.
Tesla, on the other hand, had the transformer on his side, bypassing the mechanical machines for an efficiency of around 98% – far better than Edison could wish for. Tesla and George Westinghouse built the first hydro-electric power plant in 1895 at Niagara Falls. The voltage was stepped up to a higher voltage (2500V, I believe) and therefore lower current, to provide power to nearby cities.
Edison was left to attempt to provide DC power only to large cities, locally. In order to persuade people of the time to use DC, Edison promoted the use of ac electricity for executions, even demonstrating the dangers of AC by electrocuting an elephant. In reality, AC is far safer than DC for supply and distribution.