Iberian Union
The monarchs had long wanted to unify the peninsula: They had the  visigothic monarchy in mind. Sancho III of Navarre and Alfonso VII of León and Castile both took the title Imperator totius Hispaniae, meaning "Emperor of All Hispania" centuries before.  If  Miguel da Paz (1498–1500), Prince of Portugal and Asturias had become king, the union could have been achieved earlier.  However, he died early in his childhood.