From the publisher's website:

The game is based on Spain in the 15th Century. There are twelve kingdoms, one county, one principality, and the Basque provinces. The country is made up of five ethnic groups: Spaniards, Basques, Galiciens, Catalans, and Mauren. The aristocracy, especially the Grandes, the high aristocracy, controlled events in Spain. However, the average aristocracy, the Caballeros, also enjoyed extensive powers. All regions wanted to develop their own power and influence. To this end, the Castles (Castillos) played an important role. In El Grande, each player is the Grande in one region. He is allied with 30 Caballeros. Each Grande attempts, to the benefit of Spain and for his own benefit, to extend his influence across the whole of Spain. To accomplish this, he must control the majority of Caballeros in as many regions as possible. The Grande who succeeds in this is on the path to success and winning the game.