From a geostrategic perspective, the USA's national interest in Europe is basically the same today as it was at the beginning of the twentieth century: to ensure that no single power dominates the European continent. This may not have been a crucial determinant of US involvement in the First World War, but it was certainly at the heart of US policy in the Second World War, and again in the post-1945 period, as well as throughout the era of bipolarity and rivalry between the USA and Soviet Union. Once the Cold War ended in December 1991, a dramatically different geostrategic environment was ushered in-or so it seemed at the time. In the early 1990s, the international environment in many ways resembled that of the 1920s. None of the major powers was faced by a serious military threat or by a polarizing ideological or military adversary. As in the 1920s, this was the start of an era of assorted transitions in Europe, east Asia and the Middle East in the wake of collapsed empires, while the major powers preferred to look inwards to domestic challenges, with an attendant desire to downgrade foreign policy.