Oil is an essential lubricant in your engine. It lets metal press against metal without damage. For example, it lubricates the pistons as they move up and down in the cylinders.
1 By the time of the Japanese surrender in August 1945, Korea was the second-most industrialized nation in Asia after Japan itself.  But the wartime mobilization of 1937-45 had reintroduced harsh measures to Japanese colonial rule, as Koreans were forced to work in Japanese factories and were sent as soldiers to the front.
Korea was divided at the end of WWII, with the North - now the Democratic People's Republic of Korea - under the control of the Communist Soviet Union and the South overseen by the USA. Kim Il-sung became its first Supreme Leader in 1948, followed by his son Kim Jong-il in 1994 and grandson Kim Jong-un in 2011.