Nearly 12 years after the US-led invasion of Afghanistan began, a war-weary America is getting ready to leave. But there will be little in the way of a peace dividend for the US economy once the fighting stops.

The direct costs of the war are already $700bn. The original mission was to root out al-Qaeda and the Taliban. But in 2003, the US shifted nearly all of its attention and resources to Iraq. The Taliban regrouped and strengthened in Afghanistan, making the conflict far more expensive. Meanwhile, al-Qaeda shifted operations into Pakistan, Yemen and Mali, where France this month sent troops.

US forces have struggled in Afghanistan’s mountainous terrain, where getting supplies and munitions has been a complex logistical exercise. Then came the ill-fated “surge” strategy, which put 30,000 more US troops on the ground with little if any military gain. There were 3,000 attacks on US and allied forces in 2012 – a figure little changed from 2009, when President Barack Obama’s administration decided on the change in strategy.