Korean reunification refers to the potential future reunification of the Democratic People's Republic of Korea (commonly known as North Korea), the Republic of Korea (commonly known as South Korea), and the Korean Demilitarized Zone under a single government. The process towards such a merger was started by the June 15th North–South Joint Declaration in June 2000, where the two countries agreed to work towards a peaceful reunification in the future. However, the process of reunification has met many difficulties due to ongoing tension between the two states, which have become politically and economically different since their separation in the 1940s.