That being said, if you want a united Iberia to work, then the 1580 union isn't a very good starting point to begin with. By 1580 the national consciousness and overall trajectories of Spain and Portugal had already been clearly defined - the War of the Castilian Succession, the Treaty of Alcáçovas, and the Treaty of Tordesillas had all neatly delineated the long term interests of the Avis realm of Portugal and the Trastámara realm of Castile-Aragon. The growing feelings of cultural and national estrangement between these two kingdoms would be further accentuated by their individual points of pride: the conquest of Mexico and Peru or the discovery of India and China were considered Castilian or Portuguese accomplishments, respectively, not Iberian or Spanish ones. Another factor was the Habsburg inheritance of Castile-Aragon - the Habsburgs were, after all, a dynasty of foreign extraction that had not taken part in the Reconquista, the defining Iberian cultural experience - and it took a few generations for even the Castilians and Aragonese to begin to consider their Habsburg rulers as truly Spanish. By 1580, the Castilian-Portuguese rivalry is already cemented, with the two no longer viewing each other merely as fellow Iberians, but as untrustworthy foreigners with adverse designs on one another. One can see this rivalry play out with all its disastrous effects in the East Indies, where the Castilians and Portuguese were exceedingly reluctant to offer each other assistance, resulting in the Dutch essentially making off with the greater part of the Portuguese maritime empire.