This month's devastating wave of suicide attacks in Afghanistan (including three attacks on Monday, which brought the total number to 69 since 2005) is a grim reminder that Secretary of Defense Donald Rumsfeld, under fire for his role in Iraq, has been the architect of not one but two failing wars – and of a dangerous vision for how to apply American power.

August 2002 was Afghanistan's "Mission Accomplished" moment. Mr. Rumsfeld declared the military effort "a breathtaking accomplishment" and "a successful model of what could happen to Iraq." America had routed the Taliban, disrupted Al Qaeda, and set Afghanistan on a course for stability and democracy – and it had done it Rumsfeld's way, at little cost and with minimal loss of life.

But in reality, the mission was never accomplished. Five years after Sept. 11, America's efforts in Afghanistan, as in Iraq, are unraveling. The country's government remains weak and corrupt, and it faces daunting obstacles: dismal development indicators, an entrenched opium industry, and a reinvigorated insurgency.

How did things go so wrong so quickly? Certainly Rumsfeld and his team made tactical errors, but it's hard not to trace the mistakes to a more systemic problem: a dangerously naive notion of American power that was ascendant in Washington.

The Rumsfeld doctrine, in military terms, stresses reliance on high technology and air power and downplays large ground forces. Its corollaries are that America operates best when unencumbered by international institutions, that state-building is a distraction, and that force can accomplish political objectives with few long-term repercussions.

Afghanistan was the laboratory for this new notion of warfare and national power. Rumsfeld's Pentagon wanted to demonstrate that small groups of ground forces combined with overwhelming air power could win wars – in theory, a useful approach because it limits American casualties and costs.

The doctrine's failures in Iraq are well documented. But its shortcomings in Afghanistan have received less attention because the unraveling has occurred in slow motion and with scant media attention.

The Taliban were routed by small teams of Special Forces, who directed devastating airstrikes and guided their Afghan allies on the ground. But victory was never achieved. America's Afghan proxies allowed Al Qaeda and Osama bin Laden to slip away and reestablish their operations in Pakistan. The Taliban were driven out, but were never disbanded or politically reintegrated, and their reconstituted forces, drawing from the Iraq playbook, have made this the bloodiest year yet.

Of course we will never know what would have happened if the war in Afghanistan had been handled differently: if America had taken up NATO's Article 5 declaration ("an attack against one is an attack against all") in earnest and led a genuinely multinational force; or if the expanded coalition had deployed 200,000 troops, rather than 20,000, and stabilized the whole country, rather than just Kabul; if peacekeepers from Muslim nations had been enlisted; if ground troops were in place to cut off Mr. bin Laden's escape; or if the 5th Special Forces Group had been permitted to continue its hunt for bin Laden, rather than being redeployed to prepare for Iraq.

If security had been established, the new Afghan government would have had a major head start in building on its early popularity to consolidate authority and disarm warlords and spoilers. Development projects might have won the hearts and minds of Afghans, rather than being bottled up because of insecure conditions. The hard-core Taliban might have been shattered and its more moderate backers integrated into the political process. The drug lords, who thrive on lawlessness, could have been confronted and poppy farmers provided with genuine livelihoods.

We will never know because Rumsfeld and the administration took a different tack. Washington marginalized international institutions and long insisted that the ad hoc peacekeeping force be limited to Kabul. It subcontracted security to mujahideen in the provinces. It fought a narrowly conceived war against the Taliban that combined airstrikes and civilian detentions, neither sufficiently precise and each arousing deep resentment. It bypassed the United Nations to divide responsibility for rebuilding the Afghan state among a handful of Western countries – a messy and costly endeavor made more difficult by the absence of authoritative coordination.

The result has been a steady unraveling in Afghanistan, as in Iraq. These are, to be sure, the president's wars, but they were fought under Rumsfeld's strategy. Each was predicated on unrealistic notions of what could be achieved by force, and each dismissed the importance of international legitimacy. Afghanistan is not yet lost, but what once required several ounces of prevention now requires a pound of cure.

• Carl Robichaud is a program officer at The Century Foundation in New York. A version of this piece originally appeared on The Century Foundation's website.