For many years U.S. agriculture was able to compete as a low-cost, bulk commodity supplier. Its farms were large and consolidated, enabling economies of scale. Education and a skilled extension service meant farmers could concurrently be agronomists, engineers, and marketers. Financing was sophisticated and technology was readily adopted. Countries used tariff and nontariff barriers to slow imports from the juggernaut American farmer. Then Russia took over the wheat market and Brazil increasingly dominates corn and soybeans.  America’s top five markets for agriculture each pose challenges: China: Decoupling is underway. Washington seeks to end dependence on the Middle Kingdom for solar, batteries, and previous minerals while de...