Complex sentence: The Carolingian Kingdom of Aquitaine, subordinated to the Carolingian king or (later) emperor based in Francia (Austrasia, Neustria), included not only Aquitaine proper, but also Gothia, Vasconia (Gascony) and the Carolingian possessions in Spain as well.
Split into simpler sentences: The Carolingian Kingdom of Aquitaine subordinated to the Carolingian king or (later) emperor based in Francia (Austrasia, Neustria). It included not only Aquitaine proper, but also Gothia, Vasconia (Gascony) and the Carolingian possessions in Spain as well.