Germany didn't have the power to vaporize most of the planet with the push of a button.
Noone has that power.
Just some datapoints:
+ Land area of US: 3.7 million square miles
+ Number of nukes in existence: somewhere south of 20,000
+ Size of your average nuke's "zone of destruction" *: 225 square miles
+ Total area moderately damaged by all nukes in existence: 4.5 million square miles
*Based on row 3 on this chart. Plotted with Excel, formula (where X = warhead yield in kt, and Y=land area affected) Y=3.5363 x^0.6686. Assuming x=500.
So if everyone in the world-- including the US-- were to fire upon us, you could probably wipe out most major cities, and most military bases, and do moderate damage to most buildings. You could probably also kill ~3/4 of the population of the US, which comprises ~ 5% of the world population. Of course the fallout would be a problem, but the good news is that the really nasty stuff would decay in short order.
So nukes are bad, and we dont want anyone launching "all the nukes", but thats also unlikely to happen: Targets will be military installations and silos, rather than cities and the countryside, and for that you need a lot fewer than "all the nukes".