There is that fear too because this has never happened in world history. A superpower at its peak collapsing because of internal strife. However what would they do? American allies would look in horror and likely demand the UN to send peacekeepers to stop the violence. China and Russia would look in glee at America collapsing and try to make it worse through fake news in social media, arming various faction etc. China would use the emergency to assert itself as the new superpower of the world. However American allies in Europe and Asia would reject it. You would also geopolitical ramifications. Since the US is no longer the security guarantee of the world stronger nations will start invading weaker ones. They would do this to get resources in a major economic crisis. Also use war as a way to distract people from the economic depression. This means Iran goes all out against Saudi Arabia. China goes all out seizing the South China Sea. Russia invades eastern Ukraine and Belarus, etc. Basically we return back to the law of the jungle in geopolitics. An American civil war would plunge the world into economic depression because of the economic effects of the dollar no longer seen as stable. And what makes it worse there isn't a replacement for the dollar right now. So it would be chaotic mess. What likely would happen is China tries to step in and make its currency the world reserve currency. The EU and most US allies would reject that. And what would end up happening is there would be no world reserve currency. Economics would return to a law of the jungle like back in the 16th century, This means less globalization, more protectionism, tariffs, more trade embargoes. And we have to remember alot of countries will be facing their own domestic issues in this scenario. In essence it would be the ultimate worst case scenario.
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