重要理由之一是美國需要一個敵人。

而這又出於好幾個因素:

US needs an enemy for the western world, that way US can function still as its leader. Same way, US needs Russia to lead NATO.

To bring the US which is a collection of "united states" into an unified will. In principle the US is always with a potential of splitting up. Most people are not that aware of this reality, not those leading the country.

Anxiety of the current world leader.

Character of western nations.