Although the United States and Russia have greatly reduced their stockpiles of nuclear weapons over the last two decades, there is still the lingering—and spreading—threat of nuclear annihilation.

The number of nuclear weapon states has grown to nine from six since the end of the Cold War, with India, Pakistan and North Korea joining the club. Iran’s nuclear program is believed by some to be within months of weaponizing. Meanwhile the U.S., Russia, China and other nuclear countries are competing with each other to sell “civilian” nuclear technology to eager buyers in unstable parts of the world. India, Pakistan, Turkey and the United Arab Emirates are among the customers.

While Russia’s shrinking nuclear arsenal is now thought to be relatively secure, the 9/11 terror attacks and revelations about the activities of the A.Q. Khan network have heightened concerns that weapons or fissile material could fall into the hands of rogue states or extremist groups. That risk has been increased by access to technologies that are enabling nuclear newcomers to create smaller, easily transportable weapons—so-called battlefield weapons—and by the worrisome rise of military doctrines that lower the threshold of actually using nuclear weapons.

Through this Gateway, Pulitzer Center journalists examine the emerging threats of the post-9/11 era, from an alarming new arms race between India and Pakistan to the role of the U.S. and Russia as suppliers and the spread of supposedly peaceful nuclear technology to some of the world’s most dangerous neighborhoods.