After WWI, together with the rest of Transylvania, Marosvásáshely became part of Romania and was renamed Oșorheiu. From having been an 89% Hungarian-populated city (1910), Romanian population increased throughout the latter half of the 20th century. From 1940 to 1944, as a consequence of the Second Vienna Award, the city was ceded back to Hungary.

After Hungary was occupied by Germany in 1944, a Jewish ghetto was established in the city. Oșorheiu re-entered the Romanian administration at the end of the war in October 1944. However, on 12 November 1944 General Vladislav Petrovich Vinogradov of the Soviet Red Army expelled the returning Romanian authorities from Northern Transylvania with reference to the massacres committed by members of Iuliu Maniu's so-called Maniu Guard, and the Romanian authorities were not allowed to return until the government of Petru Groza was formed on 6 March 1945.   Source: Wikipedia