In the Middle Ages, the Székelys played a role in the defense of the Kingdom of Hungary against the Ottomans in their posture as guards of the eastern border. With the Treaty of Trianon of 1920, Transylvania (including the Székely Land) became part of Romania, and the Székely population was a target of Romanianization efforts. In 1952, during the communist rule of Romania, the former counties of Mureș, Odorhei, Ciuc, and Trei Scaune (with the highest concentration of Székely population), were legally designated as the Magyar Autonomous Region. It was superseded in 1960 by the Mureș-Magyar Autonomous Region, itself divided in 1968 into two non-autonomous counties, Harghita and Mureș. In post-Cold War Romania, where the Székelys form roughly half of the ethnic Hungarian population, members of the group have been among the most vocal of Hungarians seeking an autonomous Székely region in Transylvania. They were estimated to number about 860,000 in the 1970s and are officially recognized as a distinct minority group by the Romanian government.