Slowly but surely, the barriers preventing the spread of nuclear technology and materials that can be used to make weapons of mass destruction are being eroded.

The most brazen cases involve North Korea and Iran. The former left the Nuclear Nonproliferation Treaty (NPT), conducted at least two nuclear explosive tests in the past few years and has threatened to carry out more. Iran remains in the NPT but refuses to cooperate fully with the International Atomic Energy Agency (IAEA), the United Nations nuclear watchdog, and is widely suspected of seeking nuclear weapons.

However, less obvious pressures are also undermining nuclear arms control as both big and emerging powers seek strategic and commercial gains. China is planning to provide more nuclear power reactors and fuel to Pakistan, even though Pakistan refuses to join the NPT and accept rigorous IAEA surveillance of all its nuclear facilities. In a clear sign that the deal will proceed, two Chinese state-owned companies last month signed a contract to cooperate in building the reactors to generate electricity at Pakistan's Chasma atomic complex, advancing a program that worries the United States and India.