The fall of the Soviet Union ended the European epoch, the period in which European power dominated the world. It left the United States as the only global power, something for which it was culturally and institutionally unprepared. Since the end of World War II, the United States had defined its foreign policy in terms of its confrontation with the Soviet Union. Virtually everything it did around the world in some fashion related to this confrontation. The fall of the Soviet Union simultaneously freed the United States from a dangerous confrontation and eliminated the focus of its foreign policy.
In the course of a century, the United States had gone from marginal to world power. It had waged war or Cold War from 1917 until 1991, with roughly 20 years of peace between the two wars dominated by the Great Depression and numerous interventions in Latin America. Accordingly, the 20th century was a time of conflict and crisis for the United States. It entered the century without well-developed governmental institutions for managing its foreign policy. It built its foreign policy apparatus to deal with war and the threat of war; the sudden absence of an adversary inevitably left the United States off balance.
After the Cold War
The post-Cold War period can be divided into three parts. A simultaneous optimism and uncertainty marked the first, which lasted from 1992 until 2001. On one hand, the fall of the Soviet Union promised a period in which economic development supplanted war. On the other, American institutions were born in battle, so to speak, so transforming them for a time of apparently extended peace was not easy. Presidents George HW Bush and Bill Clinton both pursued a policy built around economic growth, with periodic and not fully predictable military interventions in places such as Panama, Somalia, Haiti and Kosovo.
These interventions were not seen as critical to U.S. national security. In some cases, they were seen as solving a marginal problem, such as Panamanian dictator Manuel Noriega's drug trafficking. Alternatively, they were explained as primarily humanitarian missions. Some have sought a pattern or logic to these varied interventions; in fact, they were as random as they appeared, driven more by domestic politics and alliance pressures than any clear national purpose. U.S. power was so overwhelming that these interventions cost relatively little and risked even less.