Final answer:
The event in 1588 that strained relations between England and Spain was the defeat of the Spanish Armada. This defeat cemented English naval supremacy and secured its Protestant faith, significantly altering the balance of power in Europe.
Step-by-step explanation:
In 1588, an event that significantly strained relations between England and Spain, leading to increased tensions, was b) The defeat of the Spanish Armada. The Spanish Armada was a massive fleet assembled by King Philip II of Spain with the intention of overthrowing Protestant England and restoring Catholicism. Unfortunately for him, the armada encountered numerous difficulties, including smaller and swifter English ships that harassed the Spanish fleet, forcing a retreat. This retreat was compounded by a devastating storm famously coined as the "Protestant Wind," which largely contributed to the armada's defeat and led to a turning point in world history, facilitating the rise of English naval power and future colonial endeavors.
The defeat of the Spanish Armada not only secured English Protestantism but also opened the seas for English expansion, paving the way for its eventual colonial future in North America and beyond. By the early 1600s, England began to exert its influence over smaller islands in the Caribbean, challenging Spain's previously uncontested dominance over the New World.