The Catholic Monarchs of Spain – Isabella I of Castile and Ferdinand II of Aragon – decided, no doubt in close consultation with members of the clergy, that ordering the expulsion of Jews from the Kingdoms of Castile and Aragon and its territories and possessions by 31 July of 1492 (i.e. in a period of 3 months) was a good idea. The Alhambra Decree, or Edict of Expulsion, was duly made, keeping Spain among the fashionable kingdoms of Europe (expelling Jews was very much in vogue at that time).
It is unclear just how many Jews left Spain (most of them for North Africa or the Ottoman Empire), but estimates place the number between one and two hundred thousand, with another 50,000 or so converting to Catholicism to remain in Spain. Many thousands of Jews were died trying to leave Spain – murdered by brigands who wanted their wealth, betrayed by Spanish mariners (who overcharged them for passage and in some cases dumped them overboard to drown), or executed for remaining after the deadline without converting.
The Decree remained officially in force until Vatican Council II in 1968, and post-Franco Spain has pursued a policy of reconciliation with the descendents of expelled Jews (who now have the legal right to claim Spanish citizenship without satisfying the normal inhabitancy requirements).