The threat comes first from the continent. If they have adopted the culture of the Chinese world, the Koreans have never accepted its political control. With each attempt at occupation, they rose up, as in the summer of 612, when north of Pyongyang General Eulji Mundeok crushed the immense army dispatched by the Chinese Sui dynasty.
The intrusions of China are succeeded by those of its conquerors. After taking Beijing in 1260, the Mongols reduced Korea to the status of a satellite province for nearly a century (1270-1356), before it regained its independence. At the end of the XVI th century, it was the troops of Toyotomi Hideyoshi, the condottiere who succeeded in unifying Japan, who ravaged the peninsula twice, in 1592 and 1597, with the aim of crossing into China. It took the tactical genius of Admiral Yi Sun-sin to throw them back into the sea. Like a generation later, the Manchus in turn subjugated the country (1627 and 1637) before conquering China in 1644, Korea folds in on itself, becoming a "hermit kingdom".
With the rise of imperialism, the threat now comes from the ocean. Japan, Russia, the United States and even France want to integrate Korea into their maritime empire. It was Japan that won by taking control of the country in 1910. After its defeat in August 1945, Russia and China in the North and the United States in the South immediately regained a foothold in the peninsula, officially independent, but divided de facto in areas of influence. So nowadays, thanks to the atomic bomb, the North claims to be the only truly independent Korea.