King Henry of Portugal died without an heir, triggering a struggle over who would control Portugal and its overseas empire. Several claimants competed, including Philip II of Spain and António, Prior of Crato. The crisis set the stage for a political union of the Iberian crowns under the Habsburgs.
Spanish forces supporting Philip II defeated António’s supporters near Lisbon. The victory allowed the Duke of Alba to secure Lisbon soon after and made Philip’s claim militarily dominant on the mainland. This was a decisive step toward bringing Portugal under Habsburg rule.
The Portuguese Cortes (assembly) met at Tomar and accepted Philip as King of Portugal (Philip I), creating a personal union: the same monarch ruled separate kingdoms. The agreement aimed to protect Portugal’s laws, institutions, and overseas administration while joining the crowns. This political settlement gave the Iberian Union its legal framework.
A major naval battle near São Miguel in the Azores ended in victory for a Spanish-led fleet under Álvaro de Bazán over forces aligned with António and supported by France. Control of the Azores mattered because it helped secure Atlantic routes and protect fleets moving between Europe and overseas territories. The result weakened remaining resistance to the union.
Spanish and pro-Philip forces captured Terceira in the Azores, defeating the last major stronghold of António’s supporters. With the Azores taken, the armed phase of the succession struggle effectively ended. This helped stabilize the Iberian Union and its control over Portugal’s maritime routes.
An English-led expedition under Francis Drake and John Norris attacked Spanish-Iberian Union targets and tried to encourage a Portuguese rising against Philip. The campaign failed to restore António and did not achieve its broader strategic goals. The episode showed how the union drew Portugal into Spain’s wars and made Portuguese territory a target.
After Philip II died, his son became King of Spain and also King of Portugal (as Philip II of Portugal). The smooth succession kept the union intact and reinforced the idea that Portugal’s fate was tied to Habsburg dynastic politics. Over time, however, Portuguese complaints grew about being pulled into wider Habsburg conflicts.
Philip IV took the throne at a moment when Spain faced escalating military and financial strain, including renewed large-scale wars in Europe. These pressures pushed royal ministers to seek more money and soldiers from all parts of the composite monarchy. In Portugal, that shift fed fears that traditional rights and local control were being eroded.
Count-Duke of Olivares, the chief royal minister, advanced the “Union of Arms,” a plan to distribute defense costs across the Habsburg realms. Non-Castilian territories resisted because they saw it as an intrusion on their privileges and a step toward rule “in the style of Castile.” The policy became a major driver of political backlash in both Catalonia and Portugal.
On December 1, 1640, conspirators in Lisbon overthrew the Habsburg government’s representatives, killing Miguel de Vasconcelos and arresting the vicereine, the Duchess of Mantua. They offered the crown to João, Duke of Bragança, who became King John IV, ending the Iberian Union in Portugal. The event began a long war as Spain tried to restore Habsburg control.
The Portuguese uprising led to a sustained conflict (1640–1668) as Spain contested Portugal’s new Braganza monarchy. Portugal sought foreign recognition and support while defending its borders and overseas interests. The war turned the 1640 revolution into an international struggle with long-term consequences for Iberian power.
Not all territories tied to the Portuguese Crown followed the Braganza restoration. Ceuta, a strategic North African city, remained loyal to Philip IV of Spain, and Spanish authorities worked to strengthen that loyalty over time. This highlighted how the union’s breakup created lasting disputes over key places and identities.
Spain and Portugal agreed to peace at Lisbon, with English mediation, and Spain recognized the sovereignty of Portugal’s Braganza dynasty. The treaty ended the Restoration War and confirmed the end state created by the 1640 revolt. It closed the Iberian Union era as a political project, even though the broader Spanish monarchy continued elsewhere.
Iberian Union under the Habsburgs (1580–1640)