Metropolitan France is taken over by some sort of revolution, the government that's being revolutioned against evacuates to Algeria and secures all the French colonies. Then the Arabs (who probably won't be allowed to vote, if democracy is preserved) overthrow that government. The French Empire becomes the Algerian Empire.
But I'm not sure if Algerian rebels would be able to hold on to (or want to hold on to) all that territory.
But I'm not sure if Algerian rebels would be able to hold on to (or want to hold on to) all that territory.