An independent Korean state or collection of states has existed almost continuously for several millennia. Between its initial unification in the 7th century - from three predecessor Korean states - until the 20th century, Korea existed as a single independent country. In 1905, following the Russo-Japanese War, Korea became a protectorate of imperial Japan, and in 1910 it was annexed as a colony. Korea regained its independence following Japan's surrender to the United States in 1945. After World War II, a Republic of Korea (ROK) was set up in the southern half of the Korean Peninsula while a Communist-style government was installed in the north (the DPRK). During the Korean War (1950-53), US troops and UN forces fought alongside soldiers from the ROK to defend South Korea from DPRK attacks supported by China and the Soviet Union. An armistice was signed in 1953, splitting the peninsula along a demilitarized zone at about the 38th parallel. Thereafter, South Korea achieved rapid economic growth with per capita income rising to roughly 17 times the level of North Korea. In 1993, KIM Young-sam became South Korea's first civilian president following 32 years of military rule. South Korea today is a fully functioning modern democracy. President LEE Myung-bak has pursued a policy of global engagement since taking office in February 2008, highlighted by Seoul's hosting of the G-20 summit in November 2010. Serious tensions with North Korea have punctuated inter-Korean relations in recent years, including the North's sinking of the South Korean warship Cheonan in March 2010 and its artillery attack on South Korean soldiers and citizens in November 2010.