AMERICA invaded Afghanistan to wage war on terrorism. Once there, it found itself waging war on drugs, too. American soldiers provided security for eradication teams. American cash gave Afghan peasants incentives to grow wheat instead of poppies, and rewarded local politicians on whose turf opium production fell. In all, America has spent more than $10 billion trying to suppress the opium trade. And for what?

Afghan farmers planted 200,000 hectares with opium poppies in 2013, according to the UN—a new record (see chart). John Sopko, the American official whose job is to oversee how Uncle Sam’s money is spent in Afghanistan, told National Public Radio: “If the goal was to reduce cultivation, we failed. If the goal was to reduce opium production, we failed…If the goal was to break that narco-trafficking nexus and the corrupting influence, we have failed.”

Other analysts think the money was worse than wasted. Efforts to pull up poppies and shut down opium labs have been focused in the areas least hostile to American forces, for the obvious reason that anti-drug police are less likely to be killed there. This has displaced production into Taliban-controlled areas, argues Jeffrey Clemens, an economist at the University of California, San Diego—and therefore enriched America’s enemies.

The economics of the opium trade are stacked against the drug warriors. Demand for Afghan opium is relatively inelastic: the world’s heroin addicts cannot wait for their next fix. So if the overall supply falls (because America has suppressed cultivation in friendly areas), the price shoots up. And a lot of that extra cash flows to the Taliban who, by UN estimates, earned $100m from the drug in 2011 and 2012.