What was the main source of conflict in the 16th century that caused Spain and England to no longer be allies?

Answer 1

There were several reasons why England and Spain drifted apart.

The first was that both were growing sea powers competing for wealth and colonies in America. Spain was overwhelmingly the richest country in Europe because of the gold that its ships brought back from Spanish colonies in America. English (and other) ships would freely hunt down these ships, a special type of piracy called "privateering" because it was authorised by the English government. This made the English rich but obviously annoyed and weakend the Spanish.

The second major factor was religion. When the Catholic Mary I became Queen of England, she attempted to reverse Henry VIII's religious reforms and return the Church of England to the Catholic Church. In so doing, she called on the help of the pope and the most powerful Catholic monarch in Europe - the King of Spain. In fact, she married King Phillip II and allied England with Spain. The English people were not ferociously Protestant at this stage but they did object to what they saw as foreign interference in England. When Mary died, her successor, Elizabeth, reversed the policy on calling on Catholic countries for help and instead established her own power and the separation of the Church of England. This naturally enraged the Spanish, who received special dispensation from the Pope to invade England and kill Elizabeth.

Thirdly, England used Spain as an ally in its wars against France. Elizabeth saw that fighting France served no real purpose for England any more - England had lost most of its French territory and the French could always pay their allies the Scots to attack England. Instead it made much more sense to challenge Spanish control of the seas and control of America, so that England could gain Spain's wealth and gain colonies of its own.