Nikola Tesla left his native Europe in 1884 for the United States where he hoped that alternating current (AC) concepts would be accepted. Europe apparently preferred direct current (DC) electricity for commercial use. After failure of his Tesla Electric Company, he began independent research. He had more than 700 inventions, which included an 1881 telephone repeater and an 1888 rotating magnetic field applied to an induction, motor fed by AC. Tesla devised the split-phase, induction and synchronous motors. From 1890, he worked on high frequency current and oscillators and developed what became known as the Tesla coil.