October 24, 1870: In Algiers under the leadership of Adolphe Cremieux, France granted French citizenship to all Algerian Jews. Prior to this date, citizenship was conferred on individual Jews based on their application. Algeria had been taken over by the French and this move was part of the French program of colonization. Approximately 50,000 Jews gained French citizenship in this way. (Wikipedia)
French stamps were used for conveyance of mail from Algiers beginning in 1849. In 1924, the French post office issued stamps with the name of the colony, “Algerie” overprinted on them.
Here is an example of a 10-centime Ceres head stamp postmarked in Algiers in 1870, used probably around the same time that Cremieux effected the momentous French citizenship administrative action:
And, here is one of the first overprinted stamps of 1924: