THE second-hand clothes trade often starts with a gift: an old dress or unwanted shirt, passed on for another to use. Along the way it becomes a multi-billion-dollar industry spanning several continents. It ends at a market stall, usually in Africa. And now it is the cause of President Donald Trump’s unlikeliest trade war.

Private companies in America and Europe buy up surplus donations from charities and export them to the developing world. In 2016 east African countries resolved to phase out the trade, complaining that cheap cast-offs hurt their own nascent garment industries. America responded by threatening to impose tariffs on east African goods. Kenya, Uganda and Tanzania backed down. But Rwanda has stood fast. So on March 29th Mr Trump said he would suspend duty-free access for Rwandan apparel in 60 days.

Technically, Rwanda has no grounds for complaint. Like 39 other African countries, it enjoys access to American markets under the African Growth and Opportunity Act (AGOA), enacted in 2000. One of the eligibility criteria is that countries progressively eliminate barriers to American goods. Rwanda has done the opposite, hiking duties on second-hand clothes 12-fold. “That is almost a de facto ban on these products,” complains an American official.

East Africa accounts for over a fifth of the used-clothes market. Rwanda is only a small part of that. Its stand-off with America is not very costly for either side. In 2016, according to official statistics, Rwanda’s total used-clothes imports were only $18m (against $274m for east Africa as a whole). Its exports under AGOA were just $2m.