After the defeat of the Japanese Empire in 1945 the Korean Peninsula, under Japanese control since the 1910 was cut in two, one formed by the Democratic Peoples's Republic of Korea or DPRK, a communist nation under the leadership of Kim Il-sung and the other formed by the Republic of Korea or ROK, a democratic and capitalistic nation under the leadership of Syngman Rhee. In 1950 North Korea, supported by China and by the Soviet Union decided to attack South Korea and unite Korea once again, but a coalition force led by the UN provided the full occupation of the country and at the end both sides signed a treaty of peace and the border was put on the 45° parallel, but all this would change with the nuclear war.
A new nation
When the nuclear war happened both South and North Korea suffer from the apocalypse, the first hit with at least four targets and the second hit with only one target on the capital of North Korea, in both capitals their head of state; President Park Chung-hee of South Korea and President Kim Il-sung, killing each president and bring more chaos to the Korean Peninsula.
In the immediate time after the war both country was without a leader and leave both army without orders, in North Korea many generals fight each other one the effort of become the leader of the North Korea and after that unite Korea under a communist government, but a minority of the generals, mostly located in or near the DMZ decided to cooperate with the remains of the South Korean Army remained without orders. But luckily the Prime Minister of South Korea managed to survive and relocate the capital of South Korea in Daejeon and proclaim the Provisional Government of the Republic of Korea, the provisional government quickly gained contact with the South Korean units in other parts of Korea, and also with the help from the American troops the Provisional South Korean Armed Forces was created in order to protect the republic and from providing North Korean troops to attack the South.