Queen Isabella of Castile issues the Alhambra Decree, ordering her 150,000 Jewish and Muslim subjects to convert to Christianity or face expulsion.

Isabella I, also called Isabella the Catholic, was Queen of Castile and León from 1474 until her death in 1504. She was also Queen of Aragon from 1479 until her death as the wife of King Ferdinand II. Reigning together over a dynastically unified Spain, Isabella and Ferdinand are known as the Catholic Monarchs. Her reign marked the end of Reconquista and also the start of Spanish Empire and dominance of Spain over European Politics for the next century.

The Alhambra Decree was an edict issued on 31 March 1492 by the joint Catholic Monarchs of Spain, Isabella I of Castile and Ferdinand II of Aragon, ordering the expulsion of practising Jews from the Crowns of Castile and Aragon and its territories and possessions by 31 July of that year. Its primary purpose was to eliminate the influence of practising Jews on Spain's large formerly-Jewish converso New Christian population, to ensure the latter and their descendants did not revert to Judaism. Over half of Spain's Jews had converted as a result of the religious persecution and pogroms which occurred in 1391. Due to continuing attacks, around 50,000 more had converted by 1415. A further number of those remaining chose to convert to avoid expulsion. As a result of the Alhambra Decree and persecution in the years leading up to the expulsion of Spain's estimated 300,000 Jewish origin population, a total of over 200,000 had converted to Catholicism in order to remain in Spain, and between 40,000 and 100,000 remained Jewish and suffered expulsion. An unknown number of the expelled eventually succumbed to the pressures of life in exile away from formerly-Jewish relatives and networks back in Spain, and so converted to Catholicism to be allowed to return in the years following expulsion.^:17

Spanish and Portuguese Jews, also called Western Sephardim, Iberian Jews, or Peninsular Jews, are a distinctive sub-group of Sephardic Jews who are largely descended from Jews who lived as New Christians in the Iberian Peninsula during the few centuries following the forced expulsion of unconverted Jews from Spain in 1492 and from Portugal in 1497. They should therefore be distinguished both from the descendants of those expelled in 1492 and from the present-day Jewish communities of Spain and Portugal.