That's something different than specialization. Suppose you have enough mining production to meet half of domestic demand. Then you still have mining productio

That's something different than specialization. Suppose you have enough mining production to meet half of domestic demand. Then you still have mining production, and know how to do it, and if it was necessary you could scale it up or reduce domestic consumption somewhat from the uses that aren't as important. Whereas if you outsource all of it or nearly so, i.e. actual specialization, it's a vulnerability whether to enemy action or just a single point of failure that subjects the whole world to unexpected localized turmoil in the only place that makes that.