One reason the korean war was important is the fact that
a- it ended with an armistice and not a peace treaty
b- stalin died as a result of a gunshot during the inchon invasion and was no longer the head of the soviet union
c- nuclear weapons were not used and this set a precedent for the rest of the cold war
d- douglas macarthur became the president of the united states

Nuclear Weapons were not used and therefore set the precedent for the rest of the war. Truman, who was president at the time, wanted to stop communism at any cost. During the Korean war, he did not use nuclear weapons like were previously used to end WWII. Cold War was directly after, and since Truman didn't use any, no one else decided to. He did manage to keep communism out of South Korea (split by the 38th parallel) without the use of them. Stalin died from a stroke, although historians think he was poisoned. MacArthur was fired by Truman for not listening to him, he wasn't president. He was treated like a hero by citizens though depsite disobeying. It's non-use of nuclear weapons. :)

The answer to your question would be b