It was 1942. Across the Atlantic, vast, troubled swathes of Europe were occupied by the Wehrmacht. Millions of its civilians were displaced; millions more would pack up their belongings and flee as World War II continued to unfold.

Incalculable numbers would also do so at its bitter end, as they faced the grim prospect of life in cities such as Dresden so decimated that not one brick remained upon another, or countries like poor beleaguered Holland, where extreme food scarcity would spawn a host of transgenerational health issues. Earlier that year, General Erwin Rommels counter-offensive against the British had relentlessly pushed the Allied Forces back to the Egyptian frontier. After the Axis capture of Tobruk on 21 June, its strategic advance towards the Suez Canal and vital oil supplies would be halted by the Allies but only just - at El Alamein.

As these tactical manoeuvres played out, a Warner Bros movie called Casablanca was cobbled together in seven short weeks from 25 May to 3 August 1942. Its actors and extras were notably cosmopolitan in character not unlike the bitter global war in which many had been displaced. Madeleine LeBeau, for example, had fled Paris in 1940 with her husband, finding their way to the USA via Spain, Portugal and Canada with transit visas and obtaining small roles in Casablanca shortly after their arrival. Even Conrad Veidt, who played the German Major Heinrich Strasser, was a refugee who had fled the Nazi regime in 1933.

The casts lived experience of war, persecution and displacement was echoed in scene after scene. Desperate haggling is overheard in Ricks Caf Americain for precious Letters of Transit to enable safe passage to Portugal and then onwards to the USA or Canada. Here the Czech resistance fighter Victor Lazlo, played by Paul Henreid, palpably stiffens at the Nazis tub thumping rendition of Die Wacht am Rhein before storming downstairs and demanding that the orchestra drown them out with La Marseillaise.

Although fictional, Lazlo could feasibly have been based on a number of Czech resistance fighters; Jozef Gabk or Jan Kubi, for example, who assassinated the terrifying SS-Obergruppenfhrer Reinhardt Heydrich, Acting Governor of the Protectorate of Bohemia and Moldavia, days after the filming of Casablanca commenced. (In revenge, the Nazis razed the town of Lidice in present day Czech Republic.) Or perhaps he was modelled on Josef Balaban, Josef Man or Vclav Morvek who secretly relayed information to the Czech Government-in-Exile in London whilst carrying out courageous, sophisticated on-the-ground sabotage operations.

Casablanca attracted some favourable reviews after its premiere on 26 November 1942 - rich, suave, exciting and moving said Bosley Crowther the next day in the New York Times - and a smattering of academy awards. The timing of external events proved unusually serendipitous. In parallel with the victory by Commonwealth forces at the Second Battle of El Alamein, the US Army had captured Casablanca a few weeks earlier in the context of Operation Torch and the Allied invasion of French North Africa. (The armys reception by the French Northern African population was as hallmarked by shifting loyalties and complexities as the scene where, after the enthusiastic rendition of La Marseillaise, Lazlo is toasted by soldiers of the Vichy regime.) Then in January 1943 Casablanca played host to a conference attended by Franklin Roosevelt, Winston Churchill and Charles De Gaulle. Suddenly the name of this previously unknown town was on everyones lips.

Themes of commitment and courage permeate the movie, in the context of momentous times. Its argued that Rick Blaine, who sticks his neck out for nobody a wise policy, according to Captain Renault - symbolises the USA, turning from indifference and isolationism to engagement with the world. Other clues scattered throughout the movie point to this. Why name it Casablanca rather than Everyone comes to Ricks, the play on which provided the screenplay was based? But perhaps the Spanish meaning of Casablanca (White House) is coincidental. Elsewhere in the script, Signor Ferrari speaks of the impracticality of a policy of isolationism and in the movies final moments, Lazlo welcomes Rick back to the fight.

Some scenes are undeniably corny. The musical arrangements are a little dated, intruding into scenes in a clunky, 1940s kind of a way (oh to hear a fresh arrangement of Max Steiners fabulous score, enhanced by todays audio technology). But the movie still resonates, despite its imperfections. Why?

In lockstep with legions of bloggers and movie buffs, I think LeBeau holds the key. Her character Yvonne is spurned by Rick early on, next seen on the arm of a Nazi Officer, then glimpsed alone in Ricks Caf, before she joins with the other caf patrons in singing La Marseillaise. Real tears were in LeBeaus eyes as Yvonne cried Vive La France! Vive la Dmocratie! whilst, according to witnesses, other cast members struggled to contain theirs. A thousand vexed question marks hung in the ether; who would win the battles, how long the occupation would last, when the refugees could go home, and how much suffering there would be along the way (hint: lots).

Dying in May 2016, LeBeau is widely believed to be the last surviving member of the cast. But eighty years later, the consummate authenticity of characters such as Lazlo, Blaine and Yvonne, set against the backdrop of the most momentous war in history, has ensured the longevity of this motion picture. Even in an era saturated with sound bites, fake news, and fading, superficial memories of the 20th century. Happy birthday, Casablanca.