Historically, members of the Scared College of Cardinals came from three different groups: the nephews, Italian nobility, and crown-cardinals,. I'm going to break down these three in the description.

Cardinal-Nephews: Up until the turn of the 17th century, these cardinals were appointed by their papal uncles. Sometimes though like Cesare Borgia, they were illegitimate children.

Italian Nobility- These cardinals were drawn primarily from the Roman Black Nobility such as the Orsini and Colonna, although other Italian families such as the Sforza of Milan were in the College as well. This group of cardinals made up the bulk of the Vatican Bureaucracy. Like the Cardinal-nephews, these families dominated the College of Cardinals by virtue of their connections to previous popes.

Crown-Cardinals: This group of cardinals were generally foreigners from England, France, Castile, and Portugal who lived in their native kingdoms and only traveled to Rome for the conclaves. Though these men rarely became popes, they were royal favorites and lived lavish lifestyles and had leading positions in the kingdom. These non-Italian cardinals generally held the most prestigious archbishoprics of Europe (Lyon, Reims, Canterbury, Toledo, Krakow, Cologne, Salzburg, etc.). On some occasions like in 1903, a crown-cardinal used a monarch's veto to invalidate an election.