For nearly 20 years, Bagram Airfield was the heart of American military power in Afghanistan, a sprawling mini-city behind fences and blast walls just an hour’s drive north of Kabul. Initially, it was a symbol of the U.S. drive to avenge the 9/11 attacks, then of its struggle for a way through the ensuing war with the Taliban.

In just a matter of days, the last U.S. soldiers will depart Bagram. They are leaving what probably everyone connected to the base, whether American or Afghan, considers a mixed legacy.

“Bagram grew into such a massive military installation that, as with few other bases in Afghanistan and even Iraq, it came to symbolize and epitomize the phrase ‘mission creep’,” said Andrew Watkins, Afghanistan senior analyst for the Brussels-based International Crisis Group.

U.S. Central Command said last week that it’s well past 50% done packing up Bagram, and the rest is going fast. American officials have said the entire pullout of U.S. troops will most likely be completely finished by July 4. The Afghan military will then take over Bagram as part of its continuing fight against the Taliban — and against what many in the country fear will be a new eruption of chaos.

The departure is rife with symbolism. Not least, it’s the second time that an invader of Afghanistan has come and gone through Bagram.

The Soviet Union built the airfield in the 1950s. When it invaded Afghanistan in 1979 to back a communist government, it turned it into its main base from which it would defend its occupation of the country. For 10 years, the Soviets fought the U.S.-backed mujahedeen, dubbed freedom fighters by President Ronald Reagan, who saw them as a front-line force in one of the last Cold War battles.

The Soviet Union negotiated its withdrawal in 1989. Three years later, the pro-Moscow government collapsed, and the mujahedeen took power, only to turn their weapons on each other and kill thousands of civilians. That turmoil brought to power the Taliban who overran Kabul in 1996.

When the U.S. and NATO inherited Bagram in 2001, they found it in ruins, a collection of crumbling buildings, gouged by rockets and shells, most of its perimeter fence wrecked. It had been abandoned after being battered in the battles between the Taliban and rival mujahedeen warlords fleeing to their northern enclaves.

After dislodging the Taliban from Kabul, the U.S.-led coalition began working with their warlord allies to rebuild Bagram, first with temporary structures that then turned permanent. Its growth was explosive, eventually swallowing up roughly 30 square miles.

“The closure of Bagram is a major symbolic and strategic victory for the Taliban,” said Bill Roggio, senior fellow at the Foundation for the Defense of Democracies.

“If the Taliban is able to take control of the base, it will serve as anti-U.S. propaganda fodder for years to come,” said Roggio who is also editor of the foundation’s Long War Journal.

It would also be a military windfall.

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