Conn Hallinan, a Foreign Policy In Focus columnist, discusses how improvements in the accuracy of US submarine-based nuclear missiles are ending an era of mutually assured destruction (MAD) nuclear policy, and leading to a dangerous first-strike doctrine. Other nuclear-armed rival states like Russia and China will be forced to counter with more missiles armed with more warheads – leading to a new arms race and increasing the odds of an accidental launch leading to a widespread humanity-ending nuclear war.