Eh, that’s a false equivalency. Ancient economies had far less impact on each other, even if they did trade some things occasionally. Today, economies are far more global in an interconnected sense; if America, China or the EU have a recession, the rest of the world probably does too. The same scenario would not be true a couple thousand years ago.
Sure, but when the Roman Empire collapsed, it didn’t take the rest of the world with it. If the US went through a similar scenario, it would have a dramatic impact on pretty much everyone.