No trade impact

Working through her arguments, Grinberg established cases where trade could legitimately be conducted during conflict. It was time to turn to the evidence in historical records to find out very specifically what kind of trade occurred in wars, and under what kind of conditions.

Grinberg dug deep in British and French archives, where she found a trove of relevant documents going back to the Crimean War. She found notes from a British advisory committee in World War I that recommended banning the trade of products that could be used immediately in war, as well as banning those that could be used in war before the war was over, and those whose sales generated profits that could be used during war.

Of particular interest to Grinberg: The committee also recommended that if it took longer for the enemy to convert gains from trade into military capability than the war would last, then it made sense to trade with the enemy. “You can trade them something they can turn into a profit over a year to buy a tank, if you think the war will be over in six months,” says Grinberg. “If a state predicts a longer war, then it can add items to the prohibited trade list.”

These wartime trading policies popped up in all the archives she explored. “States do rational things,” says Grinberg. “Trade is mutually beneficial, and it makes sense for both sides to keep trade going, except under certain conditions.” At the start of World War I, for instance, Germany and allied armies frequently repositioned troops as they tried to outflank each other. During this period, merchants from combatant countries were permitted to buy and sell such products as pickaxes, shovels, and spades. But as the war ground on, armies dug into positions, and “all of a sudden, ‘entrenching tools and implements’ as the British called them, were prohibited from trade,” explains Grinberg.

There were more prohibitions for World War II, which participant nations figured would last longer. But Britain and Germany still traded with each other for products they couldn’t get anywhere else: For instance, Britain needed Germany’s precision-manufactured hosiery needles, because the specialized equipment for making the needles was unavailable in Britain for the foreseeable future.

Policy implications

With evidence from this research in hand, Grinberg began thinking through the implications. “The economic interdependence argument relies on the idea that nations don’t trade during war, and with more trading we should see less fighting.” But that’s not how it works at all, says Grinberg. “Given more interdependence and the likelihood of continued trading in conflict, the push is not toward less war, but continued trading during war.”

Her dissertation and a companion paper, “Wartime Commercial Policy and Trade between Enemies” (published in International Security), drive home the argument that “trade cannot be used as a lever to prevent war, because we have too many incentives to trade during war.” This means, for instance, that we should not assume that because the United States trades with another country, there is less possibility of war with that country. Given the tense relations between China and the U.S., two very established trading partners, this seems an important observation.