At which Olympic Games was volleyball first included as an olympic discipline?

Explanation

Volleyball is a ballgame played by two teams with six players on each team. The goal is to make the ball touch the opponents court. The court consists of two halves measuring 9x9 meters and divided by a net. The net is 2,43 meters for men and 2,24 for women. Volleyball became an Olympic discipline at the Olympics in Tokyo in 1964. The games was invented in 1895 by the American William J. Morgan.