Complex sentence: Eventually, the kingdoms of Castile and Aragon eclipsed the others in power and size through conquest and dynastic inheritance, their Crowns ultimately merging in 1469 with the marriage of the Catholic Monarchs.
Split into simpler sentences: Eventually, the kingdoms of Castile and Aragon eclipsed the others in power and size through conquest and dynastic inheritance. The Crowns of Castile and Aragon finally merged in 1469 with the marriage of the Catholic Monarchs.