What would be the outcomes of such an event? How would China and the USSR react, along with the rest of the world, and how would the Cold War continue?
Would it? Granted they supported them on the quiet and sent some pilots and planes, but are the Russians really going to end everything over North Korea? Considering that the Russians only just detonated their first bomb six months before festivities kicked off I'm not even sure that they would have enough nuclear weapons or the means to deploy them to effectively threaten the US.
He wanted to use 27 nukes. That was roughly 10% of the US arsenal at the time. An arsenal which was completely and utterly controlled by SAC (cf. The Revolt of the Admirals). There is no way of him using nukes without going through the chain of command. There is very little likelyhood of there even being nukes in the theatre at the time.
SAC are going to resist like hell the idea that an Army man could tell them where and when to use their precious bombs. The only way this is going to happen is if Truman gives the go-ahead. And that's only going to happen if the Chinese intervention gets worse - which it can't really. They outran their line of supply and by the time of the UN counterattack were utterly exhausted.
I'm pretty sure from my reading of Revolt of the Admirals that by 1949 (may even have been 1948) atomics were USAF controlled. Hence their big stink over the USN gaining control of some.
It wouldn't. Nuclear war.
As others have noted a theatre commander like MacArthur could not unilaterally order the USAF to use nuclear weapons against targets in North Korea or China.
But assuming he received approval and the weapons were used, I am not so sure WW3 would be the result.
The Korean War occurred only a few years after the first use of nuclear weapons in war and I am not sure the notion that they were an "unthinkable" option in a limited war had solidified. Presuming the attacks are made against clear tactical or strategic targets (Chinese troop concentrations, Yalu River crossing sites, etc), I think it is entirely possible the USSR - with only a few nuclear bombs at its disposal and no reliable way to deliver them to the continental USA - would sit out.
The US would unconditionally "win" the Korean War, unify the Korean penninsula, and possibly be in a position to help the Nationalists on Taiwan (who were still the widely recognized government of China and it's representative in the UN Security Council at the time) reinitiate the Chinese Civil War from a position of strength and US support. This could be iffy.
Over the long haul, such an act would be diplomatically and militarily disastrous for the USA. The image of the US would be tarnished for years to come, and the USSR would come out smelling like a rose. The precedent would be set that nuclear weapons were just another tool in the tool box which would probably lead to further use of these weapons in assymetrical situations. MAD would lose a lot of its credibility, and eventually we'd probably slide into global nuclear war, "toe to toe with the ruskis"
Nope, not till Korea. See Atomic Diplomacy During the Korean War. USAF controlled the deployment plan - and they may have had some bombs missing their fissile cores, I forget - but AEC still had custody of the actual cores.
Assuming the bomb was dropped on China, the USSR would definitely have declared war.What would be the outcomes of such an event? How would China and the USSR react, along with the rest of the world, and how would the Cold War continue?