Has North Korea declared war in 2017? North Korea has not officially declared war on any country since 1950, but has threatened to launch a "great war of justice for national reunification" and to strike the US mainland in "full-out war... under the situation where the US hurts the DPRK by force of arms," using the alternative name for North Korea. In 1950, North Korea invaded South Korea, starting the three-year Korean War which ended in 1953 with an armistice, not a peace treaty. This means that North Korea is still technically at war with South Korea. The US has 28,500 troops stationed in South Korea, while the Korean Peninsula has been divided by a 4km-wide demilitarised zone stretching 250km along the border.