This can go round and round forever. It's not practical for most countries to have a viable industry in every so-called critical good across an economy. As ano

This can go round and round forever. It's not practical for most countries to have a viable industry in every so-called critical good across an economy. As another commenter noted, it's even less practical the more complex it gets because you need to be self-sufficient in the entire stack, not just parts of it. What good is fuel refining without oil? What good is shipbuilding without mines and smelters? Without the ability to build massive shipboard diesels? Etc. Moreover, it tends to make your real friends a bit nervous when you want to make yourself independent of them, because than you have less reason to defend them. It's not to say you should make your food production dependant on them, but when your sole reaosnt to figure out how to build ship engines is so you don't need to buy them from Germany (totally random, probably wrong example) it feels a bit off. This is all ignoring the tremendous costs inherent in this sort of autarkic ideal. People enjoy the highest standards of living ever today thanks to global trade.