The Korean peninsula was part of the Japanese Empire for the first half of the twentieth century. When the Japanese surrendered, the peninsula was divided between the northern half, under Soviet administration, and the south, administered by the United States. The dividing line between the two was the 38th parallel. A communist government was established in the North, while the South was placed under the control of a western-style capitalist government. In 1950, North Korea invaded the South, and a bitter war broke out, with the United States (under the auspices of the United Nations) intervening on behalf of the South and Chinese troops fighting on the side of the North.
The war ended with both governments intact and the 38th parallel remaining as the dividing line, albeit with a demilitarized zone between the two nations. The two nations have maintained the armistice (though they have never signed a permanent treaty) since 1953. The tenuous coexistence has featured hostile posturing from both governments, and not infrequent military standoffs. Exacerbating the tensions has been the fact that South Korea has become an economic power while North Korea has become one of the poorest and easily the most repressive societies in the world. North Korea's development of nuclear weapons has also made the Korean border one of the most dangerous strategic flashpoints in the world.