Many reasons are given as to why this happened. The 17th century saw a decrease in the severity of punishments probably due to a mixture of the following factors:
Protestantism became a greater threat to Catholicism than Judaism
It was seen as more a political arm of the throne than as a defender of the faith
The venality of many inquisitors became public knowledge
The declining value of confiscated goods by the tribunals meant the Inquisition ceased to be so profitable. Fewer penitents were sent to autos de fé in the eighteenth and early nineteenth centuries, given short jail sentences. Fines did not include the total confiscation of the prisoner's property.
New ideas such as those of the of Rousseau
Spain The last Inquisition execution was a schoolteacher called Cayetano Ripoli who was garroted to death in Valencia on July 26, 1826, allegedly for teaching Deist principles. His body was put into a barrel decorated with flames and buried in unconsecrated ground. It was abolished in 1834.
Portugal, following the Liberal Revolution of 1820, the "General Extraordinary and Constituent Courts of the Portuguese Nation" abolished the Portuguese inquisition in 1821. The Marquis of Pombal was an 18th century Portuguese statesman. He was the Secretary of the State of the Kingdom of Portugal and the Algarves (the equivalent to a today's Prime Minister) to Joseph I of Portugal from 1750 to 1777. He distinguished himself by his swift action following the 1755 Lisbon earthquake and policies to improve Portugal’s economy. He weakened the grip of the Inquisition and had the Jesuits expelled. (See JEWS AND THE MARQUIS OF POMBAL))
Italy saw the restoration of the Pope as the ruler of the Papal States in 1814 and so the activity of the Papal States Inquisition continued on until the mid-19th century. The last arrest was of Edgardo Mortara (1858–1870).
Goa abolished in 1812, Mexico, Peru and Cartatgena in 1820 .
Former Spanish colonies in the Americas. The wars of independence of concluded with the abolition of the Inquisition in every quarter of Hispanic America between 1813 and 1825.
The Inquisition had lasted 600 years.
To control the Inquisition In 1542 the Pope created the Supreme Sacred Congregation of the Roman and Universal Inquisition, was established "to maintain and defend the integrity of the faith and to examine and proscribe errors and false doctrines". It served as the final court of appeal in trials of heresy and played an important part of the Counter-Reformation.
It was renamed the Supreme Sacred Congregation of the Holy Office in 1904. It is often informally called the Holy Office (e.g. Italian: Sant'Uffizio and Spanish: Santo Oficio ).
It became the Sacred Congregation for the Doctrine of the Faith (SCDF) in 1965.
In 1983 the adjective Sacred was dropped from the names of all Curial Congregations, and so it became the Congregation for the Doctrine of the Faith.
See also ‘The Popes Against the Jews’ by David Kertzer