The most influential Christian institution ever is the Roman Catholic Church, but it nearly vanished if not for the efforts of Isabella of Castile and Ferdinand of Aragón also known in Spanish history as Los reyes catolicos (The Catholic Monarchs).
At the time of the discovery of the Americas, Spain possessed La Dua Sicilia (The Two Sicilies), which was all of Italy from Rome southwards, possessed Milan, and protected the Vatican states as vassal states.
At that time, Isabella signed the decree for the Spanish Inquisition at the advice of her confessor Torquemada and with him as the chief inquisitor. The Spanish Empire and the Spanish Inquisition did more to propagate Christianity than any other single factor in the history of Christianity. They forced conversion on the west coast of North America all the way to Alaska, as well than in all other Spanish possessions in North America, Central America, South America, and the Philippines.
Pope Innocence X was the Spanish Pope that divided the World between Portugal and Spain. When Spain took over Portugal and its possessions, Spain continued its campaign of conversion in all the former Portuguese colonies.
The failed invasion of Britain by the Spanish Armada ordered by Phillip II of Spain was little more than a religious war. Spain and the Catholic Church were one for centuries and Charles I of Spain (Carlos I of Spain Carl V of Germany were the same person) presided over the Diet of Warms where Luther was tried for heresy. Holland used Protestantism as a way of liberating itself from the Catholic Spain and from Phillip II of Spain who was the son of Charles I of Spain. It is ironic that Charles I was a German Hapsburg and that his son Phillip II was born and raised in Holland.
In all, the Spanish influence in shaping and propagating Christianity is evident and ignoring it is ignoring a big part of the history and development of Christianity. Christianity today bares little resemblance to the teachings and lives of Peter, Paul, and any one in Greece or Israel at the time, and a great deal to do with how Spain shaped Christianity and how others reacted to it.