[johnnyanmac]

>it is said that one ought to focus on core competencies and let other companies handle the rest. Why shouldn’t a country do the same?

Because a country isn't a business. If a companies falls out, they move on to another company based on the market.

If a country falls out, we go to war and sanction everything. If you can't survive those sanctions, the war is lost before any blood is spilt. Or at least any blood spilt by foreign invaders; the citizens will burn down the country for you instead.