[FpUser]

>"but taken too far, isolationism is a death sentence"

I would argue that few large countries have everything to be self sufficient. For the rest - they would have to band together to avoid being at the mercy of their bigger overlords.

As for efficiencies of the past: I think they lead to a complete monopoly / near monopoly in few critical areas. The result - the monopoly power becoming a political weapon and or critical vulnerability.