Following the Alhambra Decree in 1492,and in order to eliminate their influence on Spain's large converso population and to ensure its members did not revert to Judaism, many Jews in Spain either converted or were expelled. Over half of Spain's Jews had converted to Catholicism as a result of the religious persecution and pogroms in 1391. Due to continuing attacks, around 50,000 more had converted by 1415. Those who remained decided to convert to avoid expulsion. As a result of the Alhambra decree and the prior persecution, over 200,000 Jews converted to Catholicism and between 40,000 and 100,000 were expelled. An unknown number returned to Spain in the following years.:17 The resulting expulsion led to mass migration of Jews from Spain to Italy, Greece and the Mediterranean Basin. This ca