When the nazis invaded France in 1939, they installed a "puppet" government in Vichy   through which they could continue to administer the civilian population and the French colonies, a move designed to ensure the neutrality of those colonies.  

Amongst those was Morocco. As the war progressed, Morocco became the favoured way of escape out of nazi-occupied Europe by thousands fearful for their lives.

Casablanca became the port of embarkation to America, via Lisbon (Spain and Portugal also being "neutral")

This then is the setting for one of the world's most treasured movies "Casablanca" starring of course Humphrey Bogart and Ingrid Bergman, two star-crossed lovers who meet and fall in love the middle of a war which finally wrenches them apart.

There have been many spin-offs from Casablanca including 2 attempts back in the 1960's to make a musical. Neither got off the ground.

With the Cuban crisis and the growing war in Vietnam, perhaps America was not in the mood for a musical about  a war in Europe that somehow no longer seemed relevant to their current concerns.

Since then,however,  "Casablanca" has become one of the world's favourite movies with some of the world's most famous movie lines seeming to drop out of every conversation ("Here's lookin' at you kid" and "Play it again Sam" which, incidentally, Bergaman never actually said)

What makes the movie a classic is the eternal Romeo and Juliet theme of  star-crossed lovers whose passions, once aroused are then extinguished by the hand of cruel fate.

The fact that in Casablanca this happens not just once, but twice in the course of the plot, simply adds to the piquancy of the story. Who can forget the final scene as Bogart turns from Bergman's departing aircraft and walks across the glistening wet tarmac of the mist-shrouded airport into an unkown future while his lover flies off into the night to hers.