"Le Roi De Coeur" belongs to a handful of French movies which are much more known and praised abroad (another example comes to mind:"Cybèle Ou Les Dimanches De Ville D'Avray").
In France the audience snubbed it and the critics panned it;De Broca was famous for his entertaining (not meant pejoratively)works ,such movies as "Cartouche" "L'Homme De Rio" "Les Tribulations D'Un "Chinois" En Chine" were huge blockbusters and the people were not ready for "something different"..
When he tried something different,nobody understood and the director felt compelled to return to more "accessible" stories ("Le Diable Par La queue" etc);that's why" Le Roi De Coeur" has remained unique ,very original;in the past of the French cinema,to my knowledge ,only one movie mixed the war and an insane asylum (Raymond Bernard's "Un Ami Viendra Ce Soir");Bernard's movie had good potential (who are the loonies?) which he lost in a trite patriotic finale.
Broca goes all the way:in a world gone mad, the only safe place,where people have remained sensible,is an insane asylum!the last picture -which may have inspired the ending of the much more conventional "rain man" -is revealing;this is one of the most extraordinary demonstration of the absurdity of war .
Broca had done what Richard Lester tried to do (but was not able to)in his "how I won the war" :a crazy movie in which madness rules but has its own internal logic ;terrific French cast plus English Alan Bates -who loves birds and thus is a potential pacifist plus Italian Adolfo "Largo" Celi as an English major plus gorgeous Canadian Genevieve Bujold as Coquelicot (=Poppy!).