Nobody who was around at the time is ever going to forget how the war began in the bright

blue sky of Manhattan 20 years ago.

Its end last month was tinged with the grainy greenwash of a night vision image.

The picture, taken from the back of a cargo plane, shows a lone soldier stepping off a

pitch black runway onto the loading ramp.

His silhouette is an avatar of American power made familiar over the past two decades,

hot-sized helmet, body armour, rifle in hand.

The last American soldier to leave Afghanistan, Major General Chris Donahue, Commander

of the 82nd Airborne Division, had been coordinating the evacuation of Kabul Airport.

Will American soldiers be deployed like this again?

This is Chex and Balance.

I'm John Prado, the economist to U.S.

editor, each week we take one big theme, shaping American politics and explore it in depth.

Today is American interventionism over.

The attacks on September 11, 2001 were shocking and tectonic, but America's preeminent power

remained undentied.

Retalliation was justified not just in the national interest, but in that of all humanity.

Allies rallied round.

Things feel different now.

President Biden says the retreat from Kabul marks the end of an era.

How has American power changed in the past two decades?

And how will the president deploy it in the future?

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