That's only true when excluding international trade and specialization. In the world we live in, it's more often done to ensure some sort of domestic sourcing

That's only true when excluding international trade and specialization. In the world we live in, it's more often done to ensure some sort of domestic sourcing for national security critical components. With the alternative not being that competition would spring up here, but that it would spring up there. (For values of there that are not here)