The U.S. integrated Ballistic Missile Defense System is not affective at stopping a large numbers of missiles entering the U.S. which would be the case if launched by a major power. Small nations that support terrorism are a greater concern: Iran for example knows if they fire a nuclear missile at any country, they will be retaliated against. The greater Iran nuclear threat is small nukes Iran can covertly provide foreign and domestic terrorists in America, Britain and Israel, e.g. to al Qaeda. Because small nukes have a limited scope of damage compared to big nukes, it is foreseeable Terrorists in the United States and other western countries might in intervals explode small nukes to destroy their economy and to terrorize Governments and their Citizens with the indefinite prospect of more nuke attacks. Iran would of course, deny having provided terrorists nukes: It is foreseeable fearful Americans would stop investing, stop buying products except needed to live and the stock market would plummet causing huge unemployment.