 Complete the following phrase:  Mindaugas, the duke of southern Lithuania, was among the five senior dukes mentioned in the treaty with GaliciaVolhynia. The Livonian Rhymed Chronicle, reports that by the mid-1230s, Mindaugas had acquired supreme power in the whole of Lithuania. In 1236, the Samogitians, led by Vykintas, defeated the Livonian Order in the 