Casablanca, Morocco, was a French colony that acted as a holding place for refugees escaping Nazi rule in World War II while waiting for their exit visas to Portugal.
The refugees there were of different cultures and areas of the world.
The film takes place in the 4 days leading up to the Japanese attack on Pearl Harbour on 7 December 1941. The event led directly to the USA's involvement in WWII.
Bogart's character Rick represents US foreign policy, from isolationist to intervention.