Here is a new NBER working paper:

As geopolitical tensions intensify, great powers often turn to trade policy to influence international alignment. We examine the optimal design of tariffs in a world where large countries care not only about economic welfare but also about the political allegiance of smaller states. We consider both a unipolar setting, where a single hegemon uses preferential trade agreements to attract partners, and a bipolar world, where two great powers compete for influence. In both scenarios, we derive optimal tariffs that balance terms-of-trade considerations with strategic incentives to encourage political alignment. We find that when geopolitical concerns are active, the optimal tariff exceeds the classic Mill-Bickerdike level. In a bipolar world, optimal tariffs reflect both economic and political rivalry, and may be strategic complements or substitutes. A calibration exercise using U.N. voting patterns, an estimate of the cost of buying votes in the U.N., and