To quote Ticktock: "So long as our adversaries were dependable, predictable and stable we could afford to agree not to develop a layered antimissile defense. Both the USSR and the US were able to rely on MAD (Mutual Assured Destruction) simply because neither expected the other to strike first if there were no hope of surviving the nuclear exchange. In today's world that assurance does not exist. The instability of the leadership of countries, not only N. Korea and others but the US as well, renders MAD unreliable. Layered antimissile defense is a must so long as everyone realizes that it can be overwhelmed, that many more countries today can have nuclear weapons and nuclear weapons may not only be the preview of nation states but terrorist may someday have access."