The War Might Have Started with a U.S. Army Sergeant
Stalin had wanted to push a war in Korea but he did not want an all-out war with the West. He waited until the United States had completely pulled out of South Korea before considering a move in Korea. Stalin also wanted to be sure that the Chinese would be willing to come to the aid of Korea if war happened.
The tide of the war supposedly changed when the KGB got hold of an American code-breaker who was working in the U.S. Embassy. Sgt. James “Mac” MacMillan was a U.S. Army code clerk at the U.S. embassy in Moscow, and the KGB learned that he had started dating a Soviet woman. KGB agent Sergei Kondrashev was given the assignment of convincing MacMillan to tell the KGB everything he knew.
MacMillan was pretty easy to turn. Just a few weeks after meeting with Kondrashev, he defected to the USSR in return for an apartment and money to start a new life with this Soviet girlfriend. But he knew very little about codes and wasn’t helpful, except in helping the Soviets identify which people leaving the embassy were code clerks. Once they knew who to look for, the KGB was able to locate and turn “Jack,” a code clerk who gave them the information they needed to create their own American code machine in 1949.
With the newfound ability to read American communications, Stalin believed he had found a way to advance his own goals while avoiding all out confrontation with the United States. From what he intercepted about troop movements to Japan and the perceived lack of importance of Korea, he thought the Americans would not fight hard for the country. With that information, he finally gave North Korean leader Kim Il-Sung the support he had been asking for in order to invade South Korea.