It's not that they forget. It's that the world has consistently asked for the US to help and wants the help in precisely the way they dictate (ie they want to be in control of the US). Most of the rest of the world are r/ChoosingBeggers, in other words. If the US truly did become "Fortress USA", drew back within itself and stopped helping or intervening internationally, the result would be a world where Russia runs Europe and large parts of South/Central America and China runs Asia and Africa. The fact of the matter is, Europe has given up on self defense in favor of effete internal over-regulation of every aspect of their internal lives. Asia, Africa and South/Central America are so overburdened with corrupt governments that they can barely organize themselves, let alone any sort of defense against China or Russia. The Middle East/North Africa is generally in a constant tension between wanting to be democratic or Islamic. You may not like the USA, but you need the USA.

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As an American, I would like to see the US pull back significantly and watch the world crumble for a while, just to test my predictions. I think there are a LOT of people/countries who would be FAR worse for the wear and would be desperately screaming for the USA to step in. In your more honest moments, I suspect you agree with me.