The Portuguese succession crisis of 1580 () came about as a result of the deaths of young King Sebastian I of Portugal in the Battle of Alcácer Quibir in 1578 and his successor and great-uncle Henry I in 1580. As Sebastian and Henry had no immediate heirs, these events prompted a dynastic crisis, with internal and external battles between several pretenders to the Portuguese throne; in addition, because Sebastian's body was never found, several impostors emerged over the next several years claiming to be the young king, further confusing the situation. Ultimately, Philip II of Spain gained control of the country, uniting the Portuguese and Spanish Crowns in the Iberian Union, a personal union that would last for sixty years, during which time the Portuguese Empire declined, being challenged globally during the Dutch-Portuguese War.