There are three main global transformations that brought the world order on a new stage - the stage that rules the current post-modern era. However, it started more than ten years ago, the main predominant turn happened at the very beginning. To list those are: the collapse of the Soviet Union; terrorism; and the appearance of 'rouge' states.
To point out, the prior one, which gave the starts to all others was the collapse of the Soviet Union. After the official Gorbachev's speech of dissolution , the world had stopped to be bipolar but has not yet become either multipolar nor, of course, unipolar. With the fall of the Soviet Union the United States has nobody and nothing to struggle with because its enemy (USSR) for at least forty years was an antagonist and the absolute opposite of it.
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