The Strategy of Conflict

I'm learning about the strategy of conflict from a most dry and horrid book. I'm supposed to read 150 pages by tomorrow and that isn't going to happen but I still decided I needed to stop and write this.

Determent

We must deter those countries which feel it is necessary to create weapons of mass destruction.

We must deter North Korea, Iran, Iraq, etc... from creating nuclear arms.

And yet we have nuclear warheads.

"Do as I say not as I do"

This makes no sense. Especially in the sense of nuclear weapons which destroy massive amounts of living organisms and the results of the only attack from said nuclear weapons is still permeating Japanese people today.

If North Korea launches a nuclear bomb at... oh lets say New York. New York will be destroyed. I'm sure the next thought will be lets launch our own at North Korea.

What does this accomplish?

It isn't a deterrent for us to have a nuclear bomb. People will still make them because our threat is only to send ours at them. Then what?

There's still talk that the U.S. committed a war crime by hitting Japan with nuclear weapons. So we wouldn't make that mistake again.

So why have them?