Spaz, realistically, how many total nukes would it take to fuck up the entire planet and cause the deaths of millions? 4? 5? 10?
It's not just the blast and the fallout to be concerned about, but the collapse of 21st Century civilization.
We are seeing now what a little supply problem looks like. Now imagine if there was no supply at all. Zip. Finito. Who would be sending Chinese freighters to the US or US goods to Europe? Two nukes, one in NYC and the other in Washington DC would collapse the US economy. Same for the government and financial capitols of other nations.
Add to that point, that even if it was only two nukes, both in the US, what the impact would have on the global economy. The financial crises of 1929 and 2008 would be minor in comparison.