When he received the news of the start of World War II he returned to Hungary, arriving back in October 1939.
From 1942 he was a trainee in the Department of Historical Research within the Pál Teleki Scientific Institute, where he later became a lecturer.
At the end of 1951 he received an offer for the position of Senior Lecturer at the University of Debrecen but he refused it because of the serious political situation in Hungary at that time.
He contributed to the Academy's learned journal Magyar Nyelv ("Hungarian Language").
In 1957 he introduced ideas that would later make up his magnum opus Az Árpád-kori Magyarország történeti földrajza.