with Vasil Kolarov becoming president and Dimitrov becoming Prime Minister. Free elections promised for 1946 were blatantly rigged and were boycotted by the opposition. The Agrarians refused to co-operate with the new regime, and in June 1947 their leader Nikola Petkov was arrested. Despite strong international protests, he was executed in September. This marked the Dimitrov Constitution to be introduced and also an establishment of a Communist regime in Bulgaria. Boundaries Bulgaria had its fair share of significant changes to its boundaries throughout independence to communism. Before the First Balkan War, Bulgaria didn't have control over the main parts of the Rhodope Mountains, which included settlements such as Smolyan, Kardzhali and etc. After the war, Bulgaria gained the most territory in total area, as it included the eastern parts of Macedonia, Greek Thrace and Adrianople. Due to its eagerness in Macedonia, in where they didn't obtain the rest of it, began the Second Balkan War which resulted in a harsh Bulgarian defeat. It had lost all its previous gains from the previous war, and had lost its Southern Dobruja to the Kingdom of Romania. It still kept Western Thrace and the Western Outlands. During World War I, Bulgaria joined in 1915 on the side of the Central Powers and gained a large amount of land from the Kingdom of Serbia, which included Macedonia and the sheer extensiveness around Niš. After losing, Bulgaria lost its Aegean coast, and its earned land in Serbia. During the Interwar period, no change in boundaries happened, but there was an incident at Petrich, which was the only conflict it fought internationally during this period. After pro-German prime ministers elected into office, Bulgaria entered World War II on the side of the Axis powers. After the Invasion of Yugoslavia and also of Greece, Bulgaria once again obtained a coastline to the Aegean and Macedonia with Pirot. After the Soviet invasion of Bulgaria in 1944, the Bulgarians obtained Southern Dobruja. Demographics Ethnic, lingustic and religious composition Since the population was 85% ethnic Bulgarian, there was relatively little social strife aside from the conflict between the haves and have-nots. Most inhabitants of Sofia maintained close ties to the countryside, but this did not prevent a rift between the peasants and urban class (i.e. Sofia versus everyone else), although some were the result of deliberate manipulation by politicians seeking to take advantage of traditional peasant distrust of the "effeminate