Original: The instrument was invented by a young Russian physicist named Lev Sergeivich Termen ( known in the West as Léon Theremin ) in October 1920Albert Glinsky , Ether Music and Espionage , p. 285 after the outbreak of the Russian civil war .
Simplified: It was invented by Russian inventor Léon Theremin in October 1920 after the outbreak of the Russian civil war .