If a Nuclear bomb were dropped....

[Anomalocaris]

It's not so much a contradiction as it is bad phrasing. I was continuing an earlier thought and didn't separate it from the random terrorist group line of thought. My bad.

The fact that there's a black market for certain materials doesn't mean it's not governments who are buying them. It's still quite a stretch to think a random group of people could both acquire and/or make atomic weaponry on their own.

Acquiring might well be possible.  Making is probably off the table, sure. And dirty bombs which have, ahem, fallout penetrating the DNA is another thing.

What America does with a nuclear attack on New York City is entirely dependant on the actors and circumstances, was my point. But our government will certainly strike at the first available target. It's the American Way.

Keep in mind the random group of people would likely have to test a weapon to make sure something like it would work.  This hold even for acquired rather than built weapons.   It does not seem likely a technically limited group could achieve high probability of a home made nuke actually detonating properly.  North Korea, with the resources of an entire totalitarian state, didn't quite achieve a fully successful detonation on its first try.  Even a acquired nuke would have safeguard against accidental detonation.   There is no garranty a third party trying to set it off can actually cause it to detonate properly without testing the process a few times.

Any test would instantly alert every major nation in the world.

An untested terrorist nuke is far more likely to fizzle, and serve only to focus ferocious attention on the perpetrator, then to actually detonate properly and kills hundreds of thousand of people.