The use of atomic bombs at Nagasaki and Hiroshima at the end of World War II changed the world's standards for measuring military power. Nuclear weapons can eradicate ground forces and armored divisions, and flatten cities with their awesome explosive power. In the years following World War II, arsenals of nuclear weapons were rapidly built by opposing nations, each fearing the capabilities of the other. This massive arms buildup has acted as a deterrent to full-scale war, since all the governments involved are aware of the consequences should such a war take place. The threat imposed by the huge nuclear arsenals of the world powers may one day be eradicated by the development of the Strategic Defense Initiative, or SDI, a system designed to destroy enemy missiles in flight before they can reach their targets.