The death of Portuguese king Ferdinand I in 1383 sparked the Portuguese Interregnum, where civil war erupted in Portugal and no person held the throne. Following Ferdinand’s death without a legitimate heir, his daughter, Beatriz, was forced to marry King John I of Castile, meaning Portugal would lose its independence. After three wars fought against Castile during his reign, John wished to end the rivalry between the two nations and begin a new chapter in their history, but many Portuguese were against his position. They wished to retain Portuguese independence and to remain separate from the Castilians, but they could not agree on a successor to the king. Upon his death, they could not negotiate any further, forcing them to declare war on Castile. They rallied around John of Aviz, Ferdinand’s illegitimate half brother. Although the first two years of the war went largely in John I of Castile’s favor, by 1384 John of Aviz was declared the tenth King of Portugal, and in 1385 managed to win the war against Castile. The Portuguese had the help of the English throughout the war, and with the alliance signed by the two in 1386, they developed an alliance that would be used to bring Portugal into World War Two and the 1982 Falklands War.