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If NK finally achieves nuclear capability (the ability to construct a fully operational and somewhat reliable atomic weapon), they still are in the same boat they are now. They may find they then will get even less aid from any country.
As for Iran. Same goes. Russia and China cannot afford to allow their two proxies to step over some line of demarcation so to speak. Once they demonstrate they are a known threat from the nuclear viewpoint, then they (NK,Iran) are targets.
Russian and China have a strong desire to become world class economies, energy producers etc..
In order to achieve their goals they need Canada, USA, Europe to provide them with a lot of money, by way of trade.
The two proxies are literally third rate, rather poorly managed countries from a economical point, that continue to demonstrate, they cannot on their own get their way.
There are many different ways one can look at this.
Cuba during the sixtees can be used as a prime example. They had Russian ICBM pointed at the USA. Castro was hoping up and down just like NK and Iran is now.
Notice what became of Cuba. And in this case, we where in the nuclear age. So it is not like a whole new set of equations had to be generated to analyize how best to deal with the aggressor nation. Just some thoughts.

The problem is that MAD applied equally to the Soviet client states. Castro wasn't going to do jack without Moscow's OK. MAD is based at heart on the theory that "the Russians love their children, too."

Iran and NK have demonstrated that they do not. If they get the weapons, they will use them at a time and place of their choosing. The old theories don't carry as much weight - and if we don't act fast, we will be very, very sorry.

One other thought and then I'll take off - the Russians and Chinese view us as competition for resources as much as they view us as potential markets.

It would make their life easier if we were out of commission for awhile - and then had to go back to them hat in hand after they've established themselves. If we're not the world power, they have a better shot of filling that role themselves.