When Algeria came under French rule in the 19th century, it is nearly always assumed that the Jews of Algeria were granted French nationality under the 'Decret Cremieux', whereas the Muslims were not.
In fact, all native Algerians were offered French nationality in 1865, but only the Jews chose to take up French citizenship, an academic in law at the university of Aix-en-Province, Fernand Derrida, points out.
"One should never confuse nationality and citizenship," Derrida writes in a letter to Information juive (February 2007).
The leaders of the Jewish community agreed no longer to submit to Jewish law but to French civil law. The leaders of the Muslim communities refused to give up Islamic civil law. A French citizen then, as now, could not practise polygamy, for instance.