Korean resistance groups known as Dongnipgun (Liberation Army) operated along the Sino-Korean border, fighting guerrilla warfare against Japanese forces.Some of them took part in allied action in China and parts of South East Asia.One of the guerrilla leaders was the communist Kim Il-sung, who later became the first leader of North Korea.At the end of World War II in 1945, the Korean Peninsula was divided into two zones along the 38th parallel, with the northern half of the peninsula occupied by the Soviet Union and the southern half by the United States.Nevertheless, North Korea, like its southern counterpart, claims to be the legitimate government of the entire peninsula. After the Japanese surrender at the end of World War II in 1945, Korea was divided into two zones, with the north occupied by the Soviets and the south occupied by the Americans.
A sizeable amount of the population is thought to suffer from malnutrition, parasite infestations and food and waterborne diseases.
In 1948, North Korea adopted Democratic People's Republic of Korea () as its new legal name.
In the wider world, because the government controlled the northern part of the Korean Peninsula, it is commonly called North Korea to distinguish it from South Korea, which is officially called the Republic of Korea.
An invasion initiated by North Korea led to the Korean War (1950–1953).
The Korean Armistice Agreement brought about a ceasefire, but no peace treaty was signed.