This is a report by an interview on Pakistani TV conducted with Dr. Abdul Khan who is the father of the Pakistani nuclear program.
It was started because of the Indian nuclear weapons test and because Pakistan was especially concerned about their security after East Pakistan revolted in 1971 and became Bangladesh. It was sped up because Pakistan was supporting the military activities of the Americans in Afghanistan at the time of the Soviet takeover.Khan also discusses the relationship between Pakistan and both North Korea and Iran. He would not discuss nuclear technology transfer to either of those countries, however.
The existence of Pakistan's nuclear weapons program is a major reason why the American military is currently in Afghanistan.
Dr. Khan's interview is quite illuminating. It's only about 10 pages.