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.
On June 25, 1950, North Korean forces invaded South Korea. The UN, in accord with its Charter, engaged in its first collective action by establishing the UN Command (UNC), under which 16 member nations sent troops and assistance to South Korea.