During the Renaissance, the most abundant religion was the Roman Catholic Church, centered in Rome. At the start of the 15th century, there were three popes. A council convened at Constance, and they elected a new Pope. One of the previous Popes resigned, while the other two were deposed. For a hundred years, until the Reformation, the Pope, the ruler of the Catholic Church, had almost absolute power over the rulers of Europe.
The term nepotism, although first showing up in the English language around 1669, took its meaning from the term cardinal-nephews which was the Popes practice of creating Cardinals from their family, usually nephews, as they were not supposed to have children of their own. Most of the Popes of the time were from the wealthy and influential families of Renaissance Italy. Many of the Popes of the 15th century were in some way related to the ruling family of Florence, the Mediciís. Because of these secular connections, many Popes had a lot of authority over secular government.
Several of the Popes of this time were corrupt. Most of the Cardinals and Popes of the time were younger sons, as has been the tradition for centuries. A younger son had few prospects outside the Church. Having someone in the family that was high up in the Church led to fast promotions, or even an elevated starting position within the Church. Being that most of these Cardinals and Popes were from wealthy and/or ruling families led to them feeling that they were above the rules. Several of the Popes during this time had mistresses and even children. Pope Alexander IV had four acknowledged children.
These wealthy Popes were great sponsors of the arts, which flourished during this time. This was the era when the Sistine Chapel was painted, and when the church, or a Pope in particular would commission a sculpture or painting. The Vatican is full of priceless Renaissance art today. They have works by some of the greatest artists of all times. Many great Renaissance masters made frescoes, rooms, and wall murals in the Vatican.
Up until this time, the Popeís and the Church got its revenue from the Papal-States, or the property and territory owned by the church. Most of this land had been bequeathed to them when someone died, and it generated the income the Popes needed. In the Renaissance, the Popes had to not only subsidize the artists that it commissioned for its art and architecture, but some Popes decided to expand the papal lands. The Church had a papal military, and they put it to use to increase the wealth of the Church and their families. It was during this period in time that the practice of selling indulgences became popular as a form of revenue for the papacy. If you committed a sin, after confession you could purchase an indulgence to lessen your time in purgatory. Up until this time, to gain an indulgence one had to perform specific actions to gain an indulgence from the Church.
The sale of indulgences during this time was one of the cornerstones for Martin Lutherís Reformation movement.
The corrupt Popes of the Renaissance came to an end with the sacking of Rome in 1527. After this the Church had to give up much of its secular power and even some of its religious power. This came on the heels of Martin Lutherís Ninety Five theses in 1517.