With the Incheon Landing Operation, recapture of Seoul and the offensive at the Nakdong River defense line, the UN and South Korean forces exterminated North Korean forces south of the 38th parallel.
Then, whether or not they would break through the 38th parallel emerged as a matter of keen interest.
South Korean President Lee Seung-man earlier sent a statement to the US President Harry S. Truman saying that the ultimate goal of this war should be unification.
In the statement, he expressed his belief that we should realize unification by exterminating the invaders and Koreans had the right to do so.
There was no official response from the US, but the United Nations Command gave an order for every unit to stop advancing.
President Lee, then, announced that South Korean forces would never stop advancing regardless of the UNC's decision.
In a bid to prevent any confusion in the commanding system, the Korean side explained on the necessity of capturing the hills north of the 38th parallel for military tactics and finally received an agreement from the US side.
Therefore, South Korean forces came to break through the 38th parallel on October 1, General MacArthur submitted the plan to advance north, and on September 29, the US President Harry S. Truman approved it.
On October 2, it was notified to the entire units under the UN banner.
As North Korean forces did not respond to the statements that asked the North to surrender, General MacArthur carried out the plan.
Thus, the operation to advance to the North began on October 9.