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.
In the aftermath of the Japanese occupation of Korea which ended with Japan's defeat in World War II in 1945, Korea was divided at the 38th parallel north in accordance with a United Nations arrangement, to be administered by the Soviet Union in the north and the United States in the south.