The Spanish Inquisition was established under her

Being a devout Catholic, Isabella followed the Catholic Monarchs' policy of promoting religious and racial harmony. Isabella I of Castile got her mother's religious instruction and developed into a strict devout person. It was a huge accomplishment for her to receive the title of Catholic King and Queen, along with Ferdinand. She was specifically known as Isabel la Católica, or Isabella the Catholic. She and her husband established the Spanish Inquisition in 1478 because they thought it was essential to guarantee the Church's doctrinal consistency. All Jews and Muslims in Spain were required to convert to Christianity or face expulsion. Half of the Jewish population, or 40,000 Jews, are thought to have left the country. This effort to promote togetherness resulted in significant religious tension and violence.

There is strong evidence that the founding of the Spanish Inquisition was the climax of a protracted and widespread campaign against non-Christians and unconvinced converts that had regularly taken place in Castile during the late Middle Ages. The logical outcome of the institution of the Inquisition was the exile of those Jews who resisted conversion in 1492. Nevertheless, regardless of how admirable the expulsion may have appeared at the time to attain more religious and political unity, based only on its economic ramifications, the loss of this important component in Spanish society was a grave error.