Relying on foreign nations for defense is risky, because the government doesn’t control the military assets and supply chains that it needs in the event of a conflict. Britain’s conquest of the world and robust foreign trade were two sides of the same coin, both enabled by its strong navy. In this way, this passage offers modern readers an intriguing window into the assumptions about state violence behind Smith’s economic theory: for economic activity to operate according to the market system he lays out, governments must control land, resources, and trade through force, so that they can ensure they get allocated to the right private individuals. Smith’s other example, goods that already face domestic taxes, is far more straightforward. Taxing domestic producers while allowing duty-free imports amounts to giving foreign producers an unfair leg up.