This movie was in production in Czechoslovakia in August 1968 when the Soviets invaded. Director Gene Deitch and his wife Zdenka Deitchová fled the country with the film's layouts, afraid that the Soviets would expel him but not allow his wife, a Czech citizen, to leave.
The film was written with the Israeli-Palestinian conflict in mind, but the invading Soviets interpreted it as a comment on US-Soviet relations and shortly after its release in Czechoslovakia the film was banned.