North Korea, officially the Democratic People's Republic of Korea (DPRK or DPR Korea) (Korean: 조선민주주의인민공화국, Chosŏn Minjujuŭi Inmin Konghwaguk), is a country in East Asia constituting the northern part of the Korean Peninsula, with Pyongyang the capital and the largest city in the country. The name Korea is derived from Goguryeo which was one of the great powers in East Asia during its time, ruling most of the Korean Peninsula, Manchuria, parts of the Russian Far East and Inner Mongolia, under Gwanggaeto the Great. To the north and northwest, the country is bordered by China and by Russia along the Amnok (known as the Yalu in Chinese) and Tumen rivers; it is bordered to the south by South Korea, with the heavily fortified Korean Demilitarized Zone (DMZ) separating the two. Nevertheless, North Korea, like its southern counterpart, claims to be the legitimate government of the entire peninsula and adjacent islands. Both North Korea and South Korea became members of the United Nations in 1991.