Curb Nuclear Weapons

I've wondered, both recently and before, whether any nation's nuclear weapons remain to be targeting any cities of other nations. While it could be the case that such deliberate targeting was no longer indulged in, there remains the fact that many nuclear missiles are each capable of destroying a huge amount.

Also, there is the fact that nuclear strikes against cities would, almost certainly, be regarded as illegal according to United Nations law. Why, then, do we continue to have such powerful weaponry available for use?

Some could argue that high yield weapons might be required to attack large swathes of troops and their vehicles. However, with the use of a particular yield of weapon it is not possible to downsize your attack. A far more sensible approach is to use a less powerful weapon so you can deal with the situation in a much more targeted way while, therefore, not having to destroy that which it is not necessary to destroy.