The first wave of Jewish conversion to Christianity began as a result of a pogrom against the Jews of Sivilia that started a wave of pogroms around the counrty in 1391. The Jews were forced to choose between conversion and death. About 100,000 Jews converted, while others were killed and their women were raped.

A second wave of conversion started after the 1413/4 public debate of Tortosa, in which 5 Rabbis were forced to discuss religious matters under unequal terms with a converted monk and were forced to convert before the debate was over, in order to convince the Jews that Christianity was the only true faith. About 100,000 more Jews converted.

At first,the church was satisfied with the result, assuming that the New Christians will gradually accept the new faith.Therefore,the church did not distinguish between old and new Christians and New Christians had no difficulty in becoming priests and monks, and there was no difficulty to rise to rise to the highest positions in the church. Rabbi Solomon Halevi, rabbi of Burgus, became bishop of Burgus, Bartholomeo Carranzah became bishop of Toledo and Hernando de Talavira even became Archibishop of Granada.Also,in terms of the religious perception of the Spanish Church, every conversion, voluntary or forced, was an irreversible operation. Acceptance of Christianity, according to the Spanish Church doctrine, was forever, and any attempt to return to the old faith was considered heresy and the penalty was death.

The Dominican Order of monks was the initiator for the establishment of the Spanish Inquisition. They made tireless efforts to persuade the Pope and the Spanish monarchs Ferdinand and Isabella to establish an Inquisition. In 1478 the Spanish monarchs decided to ask the Pope Sixtus the 4th to establish the inquisition. The Pope agreed to the request and sent a Papal Bull calling for the astablishment of an inquisition,, and gave the authority to control the institute to the monarchy.

According to another version it was Thomas de Torquemada who convinced the rulers to establish the inquisition. He managed to achieve his goal by telling the rulers about an event that beat waves of anger throughout the kingdom: a young Christian courted a New Christian girl.One day, when he came to visit her house he found the family having a Jewish Passover dinner.This event helped Torquemada to convince the King and the Queen that the New Christians remained faithful to their Jewish religin.

There are several versions about the time the Inquisition was established. According to one version the King signed the decree immediately, but Isabella hasitated and approved the decree only in 1480, under pressure from Torquemada. According to another version the Inquisition began to operate on 1478, but the Pope suspended its operation temporarily, until 1480.Yet, according to a third version, King Ferdinand confirmed the decree, but it needed to be approved by the Corezt(the parliament), and it was approved on 1484. Thomas de Torquemada was appointed head of the Inquisition in 1483. The Inquisition began its activities in Castilia only in 1485.

There were several reasons for the establishment of the Inquisition.The formal reason was heresy. The church suspected that New Christians remaind Jews and practiced Jewish customs in their homes.

But, hiding behind the religious rational were political and economic interests of the royal family and the church.

The Christian population watched with envy the New Christians, freed from restrictions imposed on them being Jews,exploiting their new position to advance in all aspects of life.The Christian population began to pressure the church and the royal family to examine the sincerity of the New Christians. In fact, the Old Christians continued to consider the New Christians as Jews, to see them as a foreign ethnic- racial group. Religious hatred and racism became mixed.The royal family became concerned about its status in light of public pressure, which was accompanied by pogroms against the New Christians. The fear of losing control persuaded the royal family to accept the public pressure and calm the social unrest in order to strengthen the political position of the Crown. The official union between Castilia and Aragon occured only a few years ago, in 1479, although Ferdinand of Aragon and Isabella of Castilia became married in 1469.

The decision was also influenced by Ferdinand's admiration of Niccolo Machiavelli. The King was convinced that for ensuring his rule it was necessary to consolidate and unite the kingdom under one religion.

But above all, the King had economic considerations. According to the propsed regulations the Inquisition got the right to confiscate the property of heretics and the state was going to get a large portion of that property. Since many of the New Christians were rich, the King was aware of his personal enrichment posibilities.

So, the idea behind the decision toestablish the Inquisition was to deal with infidelities as a means to ensure religoius conformity under an absolute monarchy, and to put money into the the royal treasury.