Answer: the Sudanese Civil War, which lasted from 1955 to 2005. The end of the war led to the creation of South Sudan in 2011.
Some would argue the Sudanese Civil War was actually two wars – the 1st Sudanese Civil War from 1955 to 1972 and the 2nd Sudanese Civil War from 1983 to 2005. And others would argue that since North Korea and South Korea are technically still “at war” – though no fighting has happened in over 50 years – that they get the prize.
US soldiers who defected to the DPRK during the Korean War, 1950’s
A selection of the title used to describe former North Korean leader Kim Jong-il in state media: