The Battle of Alcácer Quibir in 1578 saw the death of the young king Sebastian.
Sebastian's granduncle and successor, Cardinal Henry, was 66 years old at the time.
Henry's death was followed by a succession crisis, with three grandchildren of Manuel I claiming the throne: Infanta Catarina, Duchess of Braganza (married to John, 6th Duke of Braganza), António, Prior of Crato, and King Philip II of Spain.
António had been acclaimed King of Portugal by the people of Santarém on July 24, 1580, and then in many cities and towns throughout the country.
Some members of the Council of Governors of Portugal who had supported Philip escaped to Spain and declared him to be the legal successor of Henry.
Philip marched into Portugal and defeated the troops loyal to the Prior of Crato in the Battle of Alcântara.
 The troops occupying the countryside (Tercios) commanded by the 3rd Duke of Alba arrived in Lisbon.
The Duke of Alba imposed on the Portuguese provinces a subjection of Philip before entering Lisbon, where he seized an immense treasure; meanwhile, he allowed his soldiers to sack the vicinity of the capital.
Philip was recognized as king by the Cortes of Tomar in 1581, beginning the reign of the House of Habsburg over Portugal.
When Philip left in 1583 to Madrid, he made his nephew Albert of Austria his viceroy in Lisbon.
In Madrid he established a Council of Portugal to advise him on Portuguese affairs.

António exploited the opportunity that the war between Elizabeth and Philip presented in order to convince the English to back an amphibious assault on Portugal in April 1589.
Led by Francis Drake and John Norris, the expedition of 120 ships and 19,000 men failed due to poor planning.
At the cost of more than £100,000, the English fleet had lost around 40 ships and cost at least 15,000 men their lives.
By contrast the Spanish only lost around 900 men.

Portugal's status was maintained under the first two kings under the Union, Philip II and Philip III.
Both monarchs gave excellent positions to Portuguese nobles in the Spanish courts, and Portugal maintained an independent law, currency, and government.
It was even proposed to move the royal capital to Lisbon.
The Battle of Alcácer Quibir in 1578 saw the death of the young king Sebastian. Sebastian's granduncle and successor, Cardinal Henry, was 66 years old at the time. Henry's death was followed by a succession crisis, with three grandchildren of Manuel I claiming the throne: Infanta Catarina, Duchess of Braganza (married to John, 6th Duke of Braganza), António, Prior of Crato, and King Philip II of Spain. António had been acclaimed King of Portugal by the people of Santarém on July 24, 1580, and then in many cities and towns throughout the country. Some members of the Council of Governors of Portugal who had supported Philip escaped to Spain and declared him to be the legal successor of Henry. Philip marched into Portugal and defeated the troops loyal to the Prior of Crato in the Battle of Alcântara.  The troops occupying the countryside (Tercios) commanded by the 3rd Duke of Alba arrived in Lisbon. The Duke of Alba imposed on the Portuguese provinces a subjection of Philip before entering Lisbon, where he seized an immense treasure; meanwhile, he allowed his soldiers to sack the vicinity of the capital. Philip was recognized as king by the Cortes of Tomar in 1581, beginning the reign of the House of Habsburg over Portugal. When Philip left in 1583 to Madrid, he made his nephew Albert of Austria his viceroy in Lisbon. In Madrid he established a Council of Portugal to advise him on Portuguese affairs.
António exploited the opportunity that the war between Elizabeth and Philip presented in order to convince the English to back an amphibious assault on Portugal in April 1589. Led by Francis Drake and John Norris, the expedition of 120 ships and 19,000 men failed due to poor planning. At the cost of more than £100,000, the English fleet had lost around 40 ships and cost at least 15,000 men their lives. By contrast the Spanish only lost around 900 men.
Portugal's status was maintained under the first two kings under the Union, Philip II and Philip III. Both monarchs gave excellent positions to Portuguese nobles in the Spanish courts, and Portugal maintained an independent law, currency, and government. It was even proposed to move the royal capital to Lisbon.
Iberian Union