The dissolution of the Union of Soviet Socialist Republics (USSR) in 1991 generated a hopeful mood throughout the Western world as the Cold War ended, leaving the United States as the sole superpower. The unipolar era that followed did not bring lasting peace, however, but global uncertainty and persistent conflict. In a short period of time, the mood in the "lonely superpower" faded in the face of the terrorist attacks on 11 September 2001, the wars...