President Obama has called for a world free of nuclear weapons.

But he accepts that it might not happen in his lifetime.

Why it is so difficult to scale back these systems once they are there?

Basically, nuclear weapons are ghastly because they can not be used on any scale that matters without evaporating huge numbers of civilians as well as some small military targets.

It is easy enough for Big Powers to edge away in embarrassment from the idea of annihilating millions of civilians, since they can afford expensive new networked systems which attack military targets with unerring precision and devastation.

But for some other regimes and extremist tendencies acquiring that very ‘mass destruction’ feature of nuclear weapons is their prime negotiating goal: mess with us and something Really Bad may happen to you.

Thus Iran wants to threaten Israel with a Very Final Solution, just as Israel wants to say that anyone trying that Solution will get a similar Pretty Final Solution in return. 

North Korea’s communist tyranny wants to show that it can do what the hell it likes to increase its bargaining power and so help survive longer than it should.

Some Islamist extremists seemingly would like nothing better than to inflict mass destruction on a Western city, to show their power and demonstrate the End of the West for male chauvinist religious reasons.. 

And with undemocratic and/or weird people like that sneaking round the planet bent on buying or stealing top-end mass destructive technology, the Big Powers think that keeping a few score nuclear missiles handy ‘just in case’ is not such a bad idea.

Russia has a different problem. It is only Russia’s sprawling nuclear weapon stockpiles which give Russia true ‘superpower’ status. How can it scale back its huge nuclear arsenal as the Americans propose while it can not afford anything like the new smart-weapon systems the USA deploys? For them Obama’s proposal must be tricky news.

So, Obama wins some great headlines for being both cool and ‘peaceful’. He knows that he is making this offer from a position of unassailable military strength built up by the Republicans – and that in practice nothing much will change very fast anyway. 

Good diplomacy.