At the suggestion of the American General MacArthur, in October 1943 the heads of state of the United States and the USSR met in Moscow and agreed that the USSR would declare war on Japan once the war in Germany had ended. This decision was supported by the belief that the Japanese Empire was more vulnerable in the north, in Manchuria and Korea, than in the south, in the Philippines, where it was winning the battles.
On August 8, 1945, two days after the atomic bombing of Hiroshima by the US, the USSR declared war on Japan and the next day attacked the Korean peninsula in the north. This decision alarmed the United States, that after the atomic bombings on Japan, thus ensuring the early Japanese surrender, they were no longer so interested in the entry of the Soviet Union into the war. One day after the second atomic bombing of Japan in Nagasaki on August 10, 1945, the United States sends troops to Busan, south of the Korean peninsula. Korea, on the other hand, counted on a guerrilla of communist ideology that faced Japan and supported the measures of the USSR. The American troops were also well received at their landing in Busan, to the south.
On August 10, when preparing the general surrender of Japan, the Operations Division of the US Department of War chose the 38th parallel as the boundary of the country's defense. On August 15 the surrender was published. Joseph Stalin, in a climate of increasing tension between the United States and the Soviet Union, ordered his troops to stop north of the 38th parallel, while the US troops were located south of it. Stalin admitted the surrender of Japan and did not say anything about the division of Korea. The Americans took this act as an acceptance of it.
The North, which began to industrialize and sympathize with the Soviets, formed the socialist state of North Korea on September 9, 1948. The USSR recognized its cabinet as the only legal for the entire peninsula. Meanwhile, to the south, capitalist South Korea had been born on August 15 of the same year, then the poorest part of the peninsula. The UN organized its elections: in 1945, 93% of the steel industry and 86% of the chemical industry were in North Korea, while the South was practically only a provider of food.
The division culminated in the 1950 Korean War, which began with the invasion of the North over the South. This war accentuated the differences between USA and the USSR and indirectly led to the economic regeneration of Japan.
