Complex sentence: By this act, Pannonian Croatia and Littoral Croatia formed a united Croatian kingdom, which included the historical lands of Dalmatia (Dalmatia and most of Bosnia and Herzegovina), Pannonia (eastern Slavonia and northeastern Bosnia), and Savia (western Slavonia).
Split into simpler sentences: By this act, Pannonian Croatia and Littoral Croatia formed a united Croatian kingdom. This new kingdom included historical lands of Dalmatia (Dalmatia and most of Bosnia and Herzegovina), Pannonia (eastern Slavonia and northeastern Bosnia), and Savia (western Slavonia).