I dunno. You scared of people trying to make nukes, or 100 small, portable nukes that no one knows where they are?
How will a nuke hit the US? From a ship just outside one of our ports before it is inspected. The result will be chaos and a melt down of society. (you won't be able to go to walmart and buy stuff like food.)
When it comes to nuke war and shields from nukes its all a new stuff.... so no one can be 100% sure how will it be. You can only find it out in a real war, if a shield can protect or not, etc. ww3 wont happen, maybe its even better that nukes stabilizing the world.