The main purpose of the dissertation is to explain the signature of the Strategic Offensive Reductions Treaty - known as the Treaty of Moscow - by president George W. Bush and the unanimous approval of the resolution of advice and consent to ratification of the treaty by the U.S. Senate. These decisions are seen as the results of a bargaining game in which the national and the international levels interact and influence each other. The hypotheses indicate that the members of the U.S. executive and a huge number of the U.S. senators were interested in the treaty - which stipulates that each party shall reduce substantially the aggregate number of U.S. and Russian strategic nuclear warheads, so that it does not exceed 1,700-2,200 for each side by the end of 2012 - because it preserves the ability to define how the reductions will be implemented and to determine for themselves the structure of their strategic offensive forces, in order to respond to the new threats to their country and its allies.