"The main problem in Afghanistan is that while we have largely succeeded across the spectrum in our economic and social objectives, we have failed in our central purpose, which was to leave behind a society that was at peace with itself and its neighbors," said former Ambassador James Dobbins, who served as the U.S. special representative for Afghanistan and Pakistan in 2013-14. The event was co-hosted by the Germany embassy in Washington, the American Institute for Contemporary German Studies, the German Atlantic Council and the German Council on Foreign Relations.

"It was an accidental war" following September 11, 2001. "It was initially to punish those who committed the crime with no plans or strategy for what needs to happen after that." –Ali Jalali, former Afghan interior minister

Afghanistan's progress—measured by economic growth, increased longevity of its people, and higher literacy levels—was better than most countries for the period 2000 to 2012, according to the U.N. Development Program, Dobbins said. But the NATO-led coalition botched several opportunities to bring peace to the country, he said.

In the early years of the war, the Taliban was "ejected but not defeated" and was allowed "to reorganize, recruit, train and to push back into Afghanistan to create a substantial insurgency," Dobbins said. The coalition missed opportunities for a broad reconciliation among Afghans in 2002 when several Taliban leaders who surrendered to coalition forces were sent to U.S.-run prisons at Guantanamo or Bagram air base north of Kabul, precluding any opportunities to accommodate them in Afghanistan's political process or government, he said.

It also took a decade for the coalition to "accurately assess Pakistan's motives and intentions," which were to continue using the Afghan Taliban as "an instrument of Pakistani policy," Dobbins said.

Amid the longest war in the U.S. history, which has cost about $1 trillion, Afghanistan remains unstable. In September the Taliban briefly captured the city of Kunduz and this month attacked a market outside the Kandahar airport, which serves as a hub for military operations in the south. In October, President Obama reversed his plan to withdraw all U.S. troops by 2016, and instead keep about 5,000 troops in the country.

The decision to keep U.S. troops in Afghanistan is an "important strategic indicator of U.S. commitment to Afghanistan's security," said James Cunningham, the former U.S. ambassador to Afghanistan. "The opportunity afforded Afghanistan at this point in history is really unique and it must not be squandered. It won't come again," he said. The national unity government led by Afghan President Ashraf Ghani and Chief Executive Officer Abdullah Abdullah must "perform and demonstrate achievement," to the Afghan people,  Cunningham said.

Lessons for Interventions

The NATO-led mission and its early failings in Afghanistan have become a lesson for all other global interventions since then, said Philipp Ackermann, Germany's deputy chief of mission to the U.S. "It has certainly changed my country's approach to intervention," he said.

In the early years the effort in Afghanistan wasn't just a U.S., NATO or a western one but a global mission that included many Afghan neighbors like Iran, and India, Ackermann said. Working with a provincial reconstruction team in Kunduz in northern Afghanistan, Ackermann said he witnessed Iranians rebuilding roads and Bangladeshis helping to set up microloan programs.

The presence of many countries, each with its own practices, hampered coordination, Ackermann said. The U.S. contractor DynCorp International, for example, trained local police in Kunduz in about three weeks, whereas a German unit conducting another police training program took a much slower approach, and found the fast-paced U.S. program unacceptable, he said.

Some countries preferred to give their aid to the Afghan government, whereas Germany wanted to bypass the Afghan government and spend its development assistance directly on programs, he said. After all these years there's still no good solution on how to coordinate an international effort among different countries, Ackermann said.

Coordination between military and civilian development teams also has been lacking, Ackermann said. "You have a very, very well organized military, structured, and hierarchical with tens of thousands of soldiers and civilians working for them in a clear and structured way and at the same time you have a 100 little development agencies and civilians floating around and doing their own thing," he said.

Such differences often led the International Security Assistance Force (ISAF) to assume missions that it was not equipped to handle, such as rule-of-law training programs, Ackermann said. "The imbalance between a strong and overwhelmingly present military and development" agencies "was not resolved," he said.

An 'Accidental War'

Many of the failures of the international coalition can be attributed to an absence of planning, said Ali Ahmad Jalali, Afghanistan's interior minister from 2003 to 2005.

"It was an accidental war," Jalali said. If the attacks of Sept. 11, 2001 "hadn't taken place it's hardly imaginable the U.S. would have intervened. It was initially to punish those who committed the crime with no plans or strategy for what needs to happen after that."

The United States and its coalition allies intervened in an ongoing civil war between Afghanistan's Northern Alliance and the Taliban, he said. When the Taliban was removed from power in Kabul, the coalition invited the Northern Alliance to join the government and that forced the Taliban, which wasn't fully defeated, to wait out in neighboring Pakistan, Jalali said.

The United States then shifted attention and resources away from Afghanistan as it prepared and conducted its 2003 invasion of Iraq. The Taliban revived and resumed its war against the internationally backed government in Kabul, ultimately forcing the United States and its allies to deploy much larger forces—more than 130,000 troops by 2012—to Afghanistan.

So, Jalali said, when there was "enough time [to stabilize Afghanistan] there wasn't enough resources—but when enough resources were invested, there was no time."

'Too Ambitious'

U.S. assistance agencies, including the U.S. Agency for International Development (USAID), have failed not in collecting lessons but in incorporating them in training and practice to avoid repeating mistakes, said John Sopko, the U.S. special inspector general monitoring aid to Afghanistan.

As of March 2015 Congress has appropriated about $110 billion for Afghan reconstruction, about 60 percent of which has gone to building the country's military and police, and the remainder for development. Sopko's office has documented several cases of fraud and abuse, in both military and non-military programming, adding up to billions of dollars.

Sopko pointed to a report prepared in 1988 for USAID that examined the U.S. experience in providing civilian assistance to Afghanistan for the period 1950-1979. The report found that the program was "too ambitious both in terms of scale and timing," the U.S. "expectations were generally unrealistic" and Washington placed "too much confidence in the applicability of technological solutions to complex social and economic problems in Afghanistan."

Although the report was more than a decade old by the time the United States resumed assistance in the aftermath of the 2001 invasion of Afghanistan, the earlier lessons were never followed, Sopko said.

The Afghan experience raises a deeper question for the United States and its partners, said Andrew Wilder, an Afghanistan analyst who is USIP's vice president for Asia. "The question is not just what we did wrong, but why did we do it wrong?" he asked. "And despite knowing we're doing it wrong, why do we continue to do so? What are the incentive structures that prevent institutions from learning and changing behavior?"

Gopal Ratnam is a freelance writer on international affairs.