One reason the coproduction took so long to complete is that in 1968 the Russians invaded Czechoslovakia which caused a delay.
Although devised in France, this was actually animated in Czechoslovakia.
The first animated movie to be rated PG in the United States.
Five years in the making.
The film was an international co-production between companies from France and Czechoslovakia. Russia's invasion of Czechoslovakia in 1968 delayed production.