The Chinese warned that they'd enter the war if Macarthur went too far. He didn't listen, so they did and pushed the Allies way back past Seoul again. It took another 2-3 years of stalemate before the Armistice was finally signed.
Notice that the Armistice still holds, and the Korean War is still running after 71 years. Nobody has won that war. Nobody but the US wants to keep it running. Trump, Bolton, etc, weren't willing to guarantee Security for the North Koreans by ending the war. The North Koreans were willing to give up their nukes if the war was ended with a peace treaty. As we now know, nothing has changed.
Think of today's situation as a non-combat stalemate. much as happened in areas of trench warfare during World War one. (Both sides maintained a quiet watch-and-wait in various parts of the Front, while fierce campaigns took place in other parts of the Front.)
A question or two for you. If the Korean War is finished, why are there still 30-40 thousand US troops still occupying South Korea? Why does the US interfere with North and South Korean diplomacy? Why is it any business of the US what North and South Korea agree in, anyway?