U.S.A could wipe out life on Earth if it wanted to I doubt any country that isn't highly convinced of their God(s) will use nuclear weapons against other countries that have them in significant amounts, simply because it will be mutually assured destruction. Having a lot of nuclear weapons pretty much protects you from being attacked with them. The thought of people who care more about the afterlife than reality having nuclear bombs is scary though, they don't care about mutually assured destruction because they are convinced of their fairy tales.