Will Afghanistan collapse after the departure of American troops in 2013? That grim outcome appears all too likely. But the reason why Afghanistan may be heading toward anarchy is not simply due to the Afghan National Army’s lack of military preparedness to fight an insurgency without foreign support. Rather, some of the most challenging problems that the government must face once the US leaves will be economic.

Today, the United States and its allies provide the government of Afghanistan with the vast majority of its operating budget. American taxpayers have not only built up schools, hospitals, government ministries, and the Afghan National Army and police force; they have also paid the salaries of those who man these institutions. Further, US military and foreign assistance operations in Afghanistan support many thousands of soldiers, foreign aid workers, and contractors, who pump millions of dollars into the local economy.

What will happen when the last Americans depart? If history is any guide, “foreign assistance follows the flag,” meaning that aid spending will flee in the absence of a strong military presence. First, Americans will inevitably lose interest in Afghanistan and redirect spending to the next crisis zone; today, for example, the calamity in Syria is dominating the airwaves. Second, without American troops around to provide a modicum of security, foreign aid workers will have no choice but to leave the country; they won’t be able to work in safety (and it shouldn’t be forgotten that several hundred aid workers have already been killed during the war). As a result of the American withdrawal, both the motivation for aid spending and any possibility of monitoring aid effectiveness will quickly disappear.

An abject lesson in how economics can shape a war zone is provided by Vietnam. During the early 1970s, there were some glimmers of hope in South Vietnam following the North’s severe military defeat during the 1968 Tet offensive. The United States, however, had already grown tired of the war, and the Nixon administration embarked upon a path of Vietnamization. As America’s military and economic commitment to Vietnam declined, the weak Saigon government had no choice but to raise taxes and impose austerity measures. These policies fuelled popular opinion against the regime, helping smooth the way for the North’s successful invasion in 1975.

In preparing for its eventual departure from Afghanistan, there is much the United States could have done on the economic front but has tragically failed to implement. Incredibly, after more than ten years of war, the US has no free trade agreement with Kabul, inadvertently promoting cross-border flows with Iran and Pakistan instead. Worse, these flows consist largely of needed imports, since the US has promoted a strong Afghan currency that makes it near impossible to produce goods competitively within the country. The lack of an export-oriented industry, in turn, means that Afghanistan lacks a strong and forward-looking entrepreneurial class that could have served as a foundation for an anti-Taliban society; this is an even greater shame when one recognizes the tremendous craftsmanship that Afghan society is capable of in such sectors as woodworking and glassmaking. The US has also failed after more than a decade’s presence to help Afghanistan create a credible statistics agency or a system of “national accounts” that would track how the government’s money is being spent. This lack of transparency, in turn, enables corrupt practices to flourish. A cynic might think that America’s failure to develop more robust Afghan economic data has been one of commission rather than omission. When the history of America’s involvement in Afghanistan is written, there will be much ink spilled over military strategy and tactics. Analysts will debate whether the US should have been more aggressive in Pakistan or risked higher numbers of civilian casualties when taking the fight to the Taliban. Less attention, sadly, will be paid to the economic policies made in Washington and Kabul that were also instrumental in bringing about the demise of the Afghan regime.

Ethan B. Kapstein teaches global strategy at the Wharton School, University of Pennsylvania, and is a nonresident senior fellow at the Centre for a New American Security. A retired naval officer, he has served as an academic advisor to the Counterinsurgency Advisory and Assistance Team in Kabul. –Foreign Policy