Often, economic sanctions are related to treaties or other diplomatic agreements between states. They can revoke preferential treatment, such as MFN status or import quotas for countries that do not comply with agreed international trade rules. For political or military reasons, sanctions may also be imposed to isolate a country. For example, the United States has adopted severe economic penalties for its efforts to develop nuclear weapons, and the United States has not maintained diplomatic relations. Sanctions are not always economic. President Carter’s 1980 boycott of the Moscow Olympics could be seen as a diplomatic and cultural sanction to protest the Soviet invasion of Afghanistan. Russia retaliated in 1984, triggering a multi-boycott of the Los Angeles Summer Olympics. Although sanctions have become a common diplomatic tool for nations, especially in the decades after the end of the Cold War, political scientists say they are not particularly effective. According to a landmark study, sanctions have only about 30% chance of success. The longer the target country or individual learns how to resolve these sanctions, the more effective the sanctions will be.