Philip II had many reasons for attacking England. In part, his was a religious war against heretics. Mary Stuart, Queen of Scotland and the Catholic hope for succession to the throne of England, had been executed. With her died the chance of defeating the Protestant Reformation. Pope Sixtus V urged Philip to the Holy War, promising him financial aid.

Another reason for Philip's wrath was that English pirates, chartered by Queen Elizabeth I, had challenged Spain's dominions. English privateers captured Spanish ships carrying treasure from the New World and from Africa. This booty made up a large part of England's Royal Treasury. A climax was reached when Francis Drake sailed around the world, trading at will in Spanish territory, and was knighted by Elizabeth I on his return.

The original Spanish plan of attack was made by the foremost Spanish seaman of his time, Don Alvaro de Bazan, marquis of Santa Cruz. The plan, which called for an invading force of 556 ships and 94,222 men-at-arms, was spoiled by Drake's raids. Drake entered the harbour of Cadiz with 23 English vessels in April 1587 and destroyed or captured 38 of the Spanish ships that were to make up the Armada. He took still more ships at Cascaes Bay and off Cape St. Vincent, and Philip had to change his strategy.

The new Spanish plan of attack called for fewer ships and men. The land invasion was to be commanded by Alessandro Farnese, duke of Parma, an experienced soldier and head of Philip's occupation army in the Netherlands. Santa Cruz opposed this selection, but his resistance ended with his death in January 1588. The Armada was then placed under the command of Don Alonso Perez de Guzman, Duke of Medina Sidonia, an inexperienced warrior.

The Armada sailed from Lisbon on 20 May, 1588. After putting in at Coruna for repairs, it was sighted in the English Channel on 19 July. The English fleet that met it had 197 ships; many were small coastal vessels, so the total tonnage of the two forces was about equal.

The battle was decided by the superior speed and manoeuvrability of the long, low English ships and by their long-range firepower. The Spanish were accustomed to the Mediterranean style of fighting, which called for ramming and boarding. The English raked the Spaniards with broadsides at long range. In the first engagement, near Eddystone, a Spanish flagship was destroyed and other vessels of the Armada were severely damaged. Other battles were fought off St. Alban's head on 23 July  and off the Isle of Wight on 25 July . The Armada retreated to Calais. Medina Sidonia sent a message requesting Parma's help. Blockaded, Parma was unable to aid him.

At midnight on 28 July  eight fire ships drifted into the harbour of Calais and burst into flames. The Spaniards panicked, cut their anchor cables, and drifted near Gravelines. Attacked again, the Armada fled north, intending to sail around Ireland's west coast and return to Spain. Buffeted by gales, many ships sank or ran aground. In all, 63 Armada ships were lost. Only four had been sunk in battle.