with a high degree of regularity. States normally carry out their treaty commitments because it is in their interest to do so. A treaty is made because two or more states have a common or mutual interest in establishing a new relationship or modifying an existing one. The natural penalty for the violation of a treaty establishing or regulating a mutually desired relationship is the disruption or im­ pairment of the latter. When national policies change, clauses per­ mitting termination or withdrawal by a unilaterally given notice often serve as safety valves which prevent pressures for treaty violations from building up. But there remains a residue of situations in which a state fails to live up to its obligations under a treaty still in force.