An estimated 7,000 American troops will still remain in Afghanistan after the withdrawal, but only under a cloud of uncertainty given the nature and timing of the US president’s decision – coming just hours after the resignation of defence secretary James Mattis.

There have been no formal announcements, not even a tweet from the president. But the decision appears to be in line with Trump’s distaste for these military engagements.

The war in Afghanistan is the longest American military engagement yet, lasting 17 years.

A spokesman for Afghanistan president Ashraf Ghani said via social media, “If they (US) withdraw from Afghanistan, it will not have a security impact because in the last four and a half years, the Afghans have been in full control.”

The backlash for Trump at home was unsparing. Senator Lindsey Graham, a close ally of Trump, tweeted, “The conditions in Afghanistan – at the present moment – make American troop withdrawals a highrisk strategy. If we continue on our present course, we are setting in motion the loss of all our gains and paving the way toward a second 9/11.”

Graham had called the Syrian pull-out a “disaster” and a “stain on the honour of the US”.

Trump had campaigned against these long wars and had vowed to end them after taking the US presidency. His argument – as he said in a tweet on the Syria pull-out move – was that the US cannot be the policeman of the world and it should not be spending money and spilling American blood fighting wars for others.

An administration official said, according to The Wall Street Journal, “I think it shows how serious the president is about wanting to come out of conflicts. I think he wants to see viable options about how to bring conflicts to a close.”