What was the reason for the Spanish Armada? Why was Spain willing to invade England?

The Spanish Armada was one of the largest naval fleets in history. It was assembled and deployed by the government of Spain in 1588 in an (ultimately unsuccessful) attempt to conquer England.

Spain had many reasons to dislike England, and, during that period, conquering countries you didn't like was a relatively common activity. Today we might file a motion with the UN or negotiate a trade agreement, but back then the usual choice was to deploy a naval fleet, so that is what Spain did.

One of the main reasons was that England was Protestant and Spain was Catholic, so many other countries across Europe effectively "took sides" in this theological divide. The infamous Spanish Inquisition, where members of the Catholic Church investigated and punished all non-Catholic "heretics" they found, occurred during this time.

England, on the other hand, tried to spread Protestantism across Europe, particularly in Holland, which was controlled by Spain but seeking independence.

There was also a strategic reason for Spain's attempted invasion of England: King Phillip II wanted to deploy troops to Holland to secure Spanish control there, but knew the English Navy would resist a deployment if he transported them by sea across the English Channel. King Phillip II could not send military by land, either, as the troops would pass through France, angering the French in the process.

England was also employing privateers (a cross between mercenaries and pirates) such as Francis Drake to plunder goods from Spanish ships, particularly silver. This gave Spain an economic motive as well.