Iberian Flag with the coat of arms
The Iberian Union was a political union between the crowns of Spain and Portugal that lasted from 1580 to 1640.
Iberian Kingdom map
When Isabella I died in 1504, the Spanish Royal Court chose to crown Isabella´s daughter Joanna as queen of Spain with her father Ferdinand II. Joanna married the Austrian Habsburg Philip I, son of the emperor of the Holy Roman Empire, Maximilian I and Mary of Burgundy.
Iberian Union Empire
Joanna became insane known in Spanish as “Juana La Loca” (Joanne The Crazy) and her husband Philip was declared jure uxoris king in 1506. He died soon thereafter under unclear circumstances. Jure uxoris is a Latin term that means "by right of (his) wife". The Spanish court was unwillingly to let Ferdinad II to rule the empire.
Joanna "The Crazy" by Juan de Flandes, 1500
After the Portuguese crisis of succession, The Habsburg Dynasty was the only legal connection among all those Iberian territories. Therefore, Philip II of Austria became the Spanish emperor as well as the Iberian emperor.
Portrait of Philip II of Spain by Sofonisba Anguissola