A former US Congressman who is supposed to have played a major role in the CIA operations in Afghanistan during the Soviet occupation has revealed, in his book titled, Charlie Wilson's War, that Ronald Reagan looked the other way when Zia-ul Haq went about acquiring nuclear weapons. The logic behind letting this happen was simple, according to the book. If Zia did not help the US on the Afghanistan issue...

"The Afghan resistance would collapse. The Soviets would triumph. The Zia government would disappear and be replaced by an anti-American one in Pakistan armed with a nuclear weapon"

So, in effect the Americans armed Pakistan with nukes because they were afraid Pakistan would get the nukes from somewhere else. Interesting!!