Yes, and it still is.
There is a simple reason for this. When crowned, the monarch takes over the role of being Supreme Governor of the Church of England under Christ. Hence, the current queen is the governor of the Church of England - a protestant denomination. In addition to this she was also given the title 'Defender of the Faith' in that she is to uphold the protestant, Biblical faith against what may be seen as heresies, not only by the Roman Catholic Church (in purgatory, indulgences, over-veneration of Mary, veneration of relics, praying to dead saints etc) but also by heretical sects such as Jehovah's Witnesses.
Therefore, she, and her successors, cannot be in a position of being a Catholic when defending protestant ideals and doctrine. At the Coronation, the monarch confesses a belief in God, and vows that he/she will be true to the position that, it is believed, God has given him or her by his grace.
If you look at any British coin you will see the following surrounding the queen's head:
Elizabeth II: D G : REG : F D
This stands for Elizabeth II Deo Gratia (by the grace of God) Regina (queen) Fidei Defensor (Defender of the Faith). Therefore, having a Catholic on the throne would make the monarch's spiritual role untenable - as meaningless as having a protestant as a pope.
Spain
the catholic monarchs of Spain
It started killing the people
The pope and several Roman Catholic monarchs.
1600
Catholic monarchs are any monarchs who follow the Catholic faith. The term The Catholic Monarchs is a term that the pope used to give occassionally to monarchs who especially identified with the faith, the most notable examples being Ferdinand and Isabella of Spain.
Parliament
Spain
This is from the Latin title Catholicissimus, which prior to Charles V was rendered "Most Catholic Monarch" and after Charles V was rendered Most Catholic Majesty. According to Wikipedia, it is awarded to monarchs who in the eyes of that Pope embody Catholic principles in their personal lives and state policies. The title then remains attached to the monarchs descended from the original holder in perpetuity, unless withdrawn by a Pope. The reigning monarchs of Europe who currently carry that title are the monarchs of Belgium, Luxembourg, and Spain. Historically, this title is often used to refer to the Catholic monarchs Isabella I of Castile and Ferdinand II of Aragon. And that is how you will see it used in secular history books.
In 1500 and 1600 Roman Catholic was more dominant
the catholic monarchs of Spain
catholic and protestant
Between 1600 and 1721 europeans powers were constantly at war
It started killing the people
Queen Isabella I of Castile and King Ferdinand II of Aragon, together known as the "Catholic Monarchs," ruled Spain in 1492.
Usually Roman Catholic or Jewish or Christian.
Because Spain had the "most Catholic monarchs" who sought to preserve the faith in their country unspotted by protestant heretics.