Twenty years ago, the world's first Comprehensive Nuclear-Test-Ban Treaty (CTBT) of 1996, that prohibits nations from conducting any kind of nuclear tests, either for civilian or for military purposes, was approved by the United Nations. At that time, more than two-thirds of the General Assembly's members supported it. That number has now grown to 183. Although the support was strong, some doubted whether the treaty could actually be enforced. After all, what prevents a nation from signing the treaty and then secretly conducting underground nuclear tests?