There's nowhere to run. If America falls, or gets so involved in internal upheavals that they stop being the preeminent power in the world, everyone will suffer. All of those ethnic hatreds that the fear of American action keeps to a low boil? Pogroms everywhere. Countries with unsatisfied territorial ambitions? The armies will march, the planes will fly, the missiles will launch, hopefully non-nuclear. Countries that rely on US foreign aid, either cash or loans or even food aid? They're fucked, economic and societal collapse is always just around the corner for a lot of very fucked up countries that we support. Countries that import food from America? Say goodbye to that, with all the results that you would expect. World trade without the US Navy guaranteeing free sea access? It will be reduced to a fraction of what it is now. Countries that have massive social spending to keep their population satisfied because Big Daddy US Gov takes care of protecting them, instead of spending that welfare state money on their own militaries? Systems will crash and social services will be greatly curtailed in favor of rapid remilitarization.
I could go on for hours about this, but TLDR: If America stops projecting economic and military force because they are involved in a long crisis, it will negatively affect every country on earth. Either through primary effects or through secondary or tertiary follow-on effects. An American collapse would lead to the collapse of many other countries, especially those that are only marginally real countries and are always on the verge of collapse at the best of times.
Happy Thanksgiving, kiwis! Fight for what you believe in and strive for the future that you want to see.