Isabella I of Castile and Ferdinand II of Aragon, the Catholic monarchs of Spain, issue the Alhambra Decree. All Jews living in Spain and any territories are ordered to leave or convert to Christianity within two months. Inquisitor-General Tomas Torquemada has been pushing them to do this, but they only now agree because with the unification of Spain completed, the Jews are expendable. The Alhambra Decree won't be rescinded until 1968.
Jews had lived on the Iberian peninsula since Roman times and there are currently around 150,000 Jews in Spain. Under Muslim rule they had a protected status and could live in security. Under Christian rule, however, they experience continuing suspicion and persecution.
The ultimate goal of Ferdinand and Isabella is to establish religious purity in Spain, something they had already taken significant steps towards after recapturing Granada from the Moors. The official reason for the expulsion is that the Jewish community has been influencing earlier converts to revert back to Judaism, but a more realistic explanation points towards the desire to appropriate Jewish property and money.