The Korean War was an escalation of border clashes between two rival Korean regimes, each of which was supported by external powers; each tried to topple the other through political and guerilla tactics. In a narrow sense, some may refer to it as a civil war, though many other factors were at play. After failing to strengthen their cause in the free elections held in South Korea during May 1950 and the refusal of South Korea to hold new elections per North Korean demands, the communist North Korean Army moved south on June 25, 1950 to attempt to reunite the Korean peninsula, which had been formally divided since 1948. The conflict was then expanded by the United States and the Soviet Union's involvement as part of the larger Cold War. The main hostilities were during the period from June 25, 1950 until the armistice was signed on July 27, 1953. In the early stages of the war, President Harry Truman sometimes described the conflict under the aegis of the United Nations as a "police action" rather than use the term war.