Remember at the time of the Korean War the US was at the height of it's power - it had just a few years earlier managed to defeat the Axis Powers in wide ranging theatres such as Europe and the Far East.
It was unchallenged except by the Soviet Union, and even they did not have the capacity to challenge the economic and industrial power of the US.
Also it was not the US alone, it had many countries supporting it in the so-called United Nations forces. And if I can be frank the North Koreans were pretty useless, so it was the PLA - that fought one of the global super powers and much of it's allies single-handedly.
I would advise our indian friends to not mess with a nation like that.