Politics1 October 1953
ROK–US Mutual Defense Treaty
After the armistice, South Korea and the US signed a mutual defence treaty, the legal basis for stationing US troops in Korea.

LIFE Magazine · CC BY-SA 4.0 · Source
The Rhee government, which opposed the armistice, demanded security guarantees, and the treaty was signed in Washington on 1 October 1953 (in force November 1954). The parties would act together against armed attack, and US forces could be stationed in and around Korea.
It gave US Forces Korea their legal basis, and US economic and military aid continued.