Most gripping, however, was the sound. The more aliens a player shot, the faster they approached their drumbeat quickened, the tension mounted. Ironically, says Bill Adams, director of game development for Midway Manufacturing Co., of Chicago, Ill., which licensed Space Invaders for sale in the United States, these features of the game were accidental. The game’s components were revolutionary as well, for it was the first Japanese game to use a microprocessor. Although a handful of shooter games preceded Space Invaders, its runaway success, innovative features, compelling graphics, and elemental themes captured the public imagination, spurring many imitators and a craze for arcade games, first in Japan and then around the world. Its success prompted other Japanese companies to join the video game market.