Former U.S. Secretary of State Henry Kissinger says that a U.S. diplomatic decision under President Harry Truman’s administration was linked to Joseph Stalin’s approval of North Korean founder Kim Il-sung’s plan to invade South Korea.

In his latest book “On China,” Kissinger said that the Soviet Union leader gave his approval after taking into consideration the U.S.’ new defense line in the Northeast Asian region, which excluded the Korean Peninsula. Stalin learned of the defense line through a document obtained by the Soviet Union's spy network.

Kissinger said Stalin had initially opposed Kim’s plan to launch a war on the Korean Peninsula, but that the Soviet leader gave Kim the nod in April 1950, believing that the U.S. would not intervene.