The way war is thought about and conceived has radically changed since the atomic bombs dropped over Hiroshima and Nagasaki marked he end of World War II. A war between big powers can no longer be conceived according to Von Clausewitz's classic definition, that is as the continuation of a state's foreign policy by different means. The new weapon's mass destruction potential was bound to affect not only war tactics but also military strategy and international relations. NATO and the Warsaw Pact - the two blocks created after the Potsdam conference - were bound to balance their power relationships depending on the existence of weapons with a high mass destruction potential.
A first consequence of this new strategy was the Cold War. As a second consequence, no world wars broke out for more than 40 years. Some international relations scholars in the Cold War period, such as Kennet Waltz, argued for the bipolar model and its usefulness in a world governed by the logic of Anarchy. In 1979, in Theory of International Politics, Waltz argued that the countries equipped with nuclear weapons may have a stronger incentive to prevent war than the states with conventional armaments. In 1981 he published The Spread of Nuclear Weapons: More May be Better, a definite stance for nuclear weaponry increase as a means of stability between the two superpowers.
Since 1989, the pulling down of the Berlin wall followed by the dissolution of the Warsaw Pact and the Soviet Union collapse have deeply changed the geo-strategical outlook. The Cold War was unexpectedly over and some of its fundamental players had disappeared. The role of NATO itself - trained to confront a foe no longer existed - was being seriously put into question.
Within this new and more complex situation, a trend to non-proliferation emerged, that is elimination of the nuclear threat by scaling down and eventually eliminating all nuclear weapons. This trend is based on two approaches both aimed at peace-keeping: disarmament and control over arms build-up.
1. From a strategical standpoint, disarmament is based on the assumption that the existence of weapons is not a consequence but rather a fundamental cause of uncertainty and conflicts. According to this approach, by reducing or - better still - eliminating armaments on a global scale, peace would be achieved. Obviously, in a world governed by Anarchy, where there is no authority to settle international disputes, disarmament gives way to a security dilemma. Any state that is 'left to its own resources' perceives a real or would-be threat (i.e. defence weapons in a neighbouring state) and is thus faced with the security dilemma. Then, lacking international guarantees, it will decide to keep its stockpile - nuclear or conventional as it may be.
2. Control over arms build-up is a different approach. It is based on the assumption that the causes and the very nature of conflicts are so strong they cannot be eliminated. The existence of stockpiles is not a cause but rather a consequence of international pressures. Nuclear or conventional weapons are not the cause of wars, but they basically concur in increasing the security dilemma. An uncontrolled armament increase may contribute to turn a crisis into a war. Control over arms build-up aims at keeping the crisis level below the threshold likely to end up in a war.
In view of this premise, it is in the interest of the states which maintained their nuclear stockpiles to limit the number of states that resort to nuclear weapons to increase their armaments. Any rise in this class of countries would lessen the power of the states equipped with nuclear weapons and would seriously threaten world stability. Although the existence of five nuclear powers does not prevent the risk of a nuclear war, whatever might happen, the world order is more stable if the number of states with no nuclear stockpiles stays unchanged. In this perspective, …