Complex sentence: These three cities were the core of the Nasrid dynasty and its Emirate of Granada, which was a vassal state of Castile, until the kingdom was finally taken by the Catholic Monarchs in 1492.
Split into simpler sentences: These three cities were the core of the Emirate of Granada, ruled by the Nasrid dynasty. Granada was a vassal state of Castile, until finally taken by the Catholic Monarchs in 1492.