Complex sentence: Pannonia was the plain which lies to its north, from the mountains of Illyria/Dalmatia to the westward bend of the River Danube, and included modern Vojvodina (in northern Serbia), northern Croatia and western Hungary.
Split into simpler sentences: Pannonia was the plain which lie to its north, from the mountains of Illyria/Dalmatia to the westward bend of the River Danube. It was in the modern Vojvodina (in northern Serbia), northern Croatia and western Hungary.