Francis Burkle-Young defines a crown cardinal as one "elevated to the cardinalate solely on the recommendation of the European kings and in many cases without having performed any service at all for the advancement of the Church.
[6] Opposition to national cardinal protectors arose in the fifteenth century due to the perceived conflict of interest, and Pope Martin V attempted to forbid them entirely in 1425.
[7] Such protectorships were first openly permitted by popes Innocent VIII and Alexander VI, both of whom required the explicit written consent of the pontiff for a cardinal to take up a "position of service to a secular prince".
[10] The first explicit reference to protectorship pertaining to a nation-state dates to 1425 (the Catholic Encyclopedia says 1424[11]) when Pope Martin V forbade cardinals to "assume the protection of any king, prince or commune ruled by a tyrant or any other secular person whatsoever.
[13] In the case of Spain, France, and Austria, from the 16th to 20th centuries, crown-cardinals had the prerogative to exercise the jus exclusivae, that is, to veto a candidate for the papacy deemed "unacceptable" by their patron.
[1] Austrian crown-cardinal Carlo Gaetano Gaisruck reached the papal conclave of 1846 too late to exercise the veto against Giovanni Maria Mastai-Ferretti, who had already been elected and taken the name Pius IX).