In August 1948 the Republic of Korea (R.O.K.) was established, with Syngman Rhee as the first president. North Korean troops invaded the south in June 1950, starting the three-year Korean War. An armistice ended the war in 1953, but a permanent peace treaty has never been signed. In the following decades, South Korea experienced political turmoil under autocratic leadership. President Syngman Rhee was forced to resign in April 1960 following a student-led uprising. The leadership of President Chang Myon ended after only one year when Major General Park Chung-hee led a military coup. Park's rule, which resulted in tremendous economic growth and development but increasingly restricted political freedoms, ended with his assassination in 1979. Subsequently, a powerful group of military officers, led by Lieutenant General Chun Doo-hwan, declared martial law and took power. Throughout the Park and Chun eras, South Korea developed a vocal civil society that led to strong protests against authoritarian rule. Intensified pro-democracy activities ultimately forced political concessions by the government in 1987, including the restoration of direct presidential elections. In 1987, Roh Tae-woo, a former general, was elected president, but additional democratic advances during his tenure resulted in the 1992 election of a long-time pro-democracy activist Kim Young-sam, who became Korea's first civilian elected president in 32 years. The 1997 presidential election and peaceful transition of power marked another step forward in Korea's democratization when Kim Dae-jung, a life-long democracy and human rights activist, was elected from a major opposition party. The transition to an open, democratic system was further consolidated in the following years. In 2002 Roh Moo-hyun was elected president, and in 2007 former business executive and Mayor of Seoul Lee Myung-bak was elected the new president of South Korea. Since the 1960s, South Korea has transformed from an agricultural-based economy into an industrialized and high-tech modern economy. It is now the 13th largest economy in the world.