Since it lacks modern day official recognition, Castile no longer has clearly defined borders. Historically, the area consisted of the Kingdom of Castile. After the kingdom merged with its neighbours to become the Crown of Castile and later the Kingdom of Spain, when it united with the Crown of Aragon and the Kingdom of Navarre, the definition of what constituted "Castile" gradually began to change. Its historical capital was Burgos. In modern Spain, it is generally considered to comprise Castile and León and Castile–La Mancha, with Madrid as its centre. West Castile and León, Albacete, Cantabria and La Rioja are sometimes included in the definition (controversial for historical, political, and cultural reasons).