The US would have no real reason to unless as a retaliatory strike against someone else launching
China is in a geographically bad location to attempt a first strike (land borders with other major nuclear powers) and would invoke an all out invasion on them. They also fear US anti-ballistic missile capability (we can intercept and shoot down theirs, they can't ours)
Russia wouldn't dare either as thanks to cold war, probably 90% of everyone elses nukes are already aimed at them anyways...
Israel probably has as many nukes as the US (mostly smaller tactical yield), but would probably only launch in retaliation as it wouldn't be in their interest to nuke a neighbor that's "upwind" of them...
The muslim countries with nukes wouldn't dare simply because they have so few... with small yields (they "might" be able to take out a city or two)... as the western nations would retaliate full force (with enough to wipe their country's completely off the earth ten times over)
North Korea is about the only country stupid enough to try it simply because they're led by a moron with absolutely no experience at strategy nor full on war... (pyongyang would get vaporized in mere minutes, him along with it...)