Portuguese Interregnum Crisis of 1383-1385

Timeline

1. 1383Lisbon · LisbonFerdinand I died in October 1383 with no male heirs. His daughter Beatrice had already married John I of Castile; the widowed queen Leonor Teles served as regent and leaned toward Castile. John, Master of Aviz and the king's illegitimate brother, allied with the nobility and citizens of Lisbon and other cities as the independence faction, refusing Castilian annexation of Portugal; the interregnum crisis officially broke out.
2. 1383–1384Lisbon · LisbonA popular uprising broke out in Lisbon in December 1383, overthrowing Leonor's regency faction. John was acclaimed Defender of the Realm (Defensor do Reino), gaining support from the urban merchant class and some nobles. John I of Castile claimed the Portuguese throne as Beatrice's husband, and the two sides entered armed confrontation, with Castilian forces beginning to invade northern and central Portugal.
3. 1384Atoleiros · AlentejoOn April 6, 1384, the Portuguese commander Nuno Álvares Pereira defeated the Castilian invading army at Atoleiros, winning against the odds. Using defensive square tactics, the battle heavily damaged the Castilian cavalry, temporarily halting Castile's offensive on the southern frontier and buying Portugal time to organize defenses and seek foreign aid.
4. 1385Aljubarrota · Leiria DistrictOn August 14, 1385, John and Nuno Álvares Pereira led about 6,500 Portuguese troops against some 31,000 Castilians at Aljubarrota. The Portuguese held favorable terrain, using infantry pike formations together with English longbowmen to annihilate the Castilian main force. This was one of the decisive medieval battles of Iberia, completely shattering Castile's attempt to annex Portugal.
5. 1385Coimbra · CoimbraThe Cortes of Coimbra convened in April 1385, before the great victory at Aljubarrota; representatives of the three estates, invoking Salic law tradition and the principle of national self-determination, rejected Beatrice's claim and formally acclaimed John as King John I of Portugal. The House of Aviz was thereby established, the interregnum crisis ended with Portuguese independence and consolidated sovereignty, laying the foundation for the subsequent Age of Discovery.