In 2001 the point was a “war on terror”. The atrocities of 9/11 demanded decisive action, and Afghanistan a sanctuary for al-Qaeda and the group's leader Osama bin Laden. The Taliban were removed from power, a new government was democratically installed and, in 2011, bin Laden was killed.
Having achieved relative stability in this notoriously splintered country, the US-led coalition could have maintained a presence to keep the peace in Afghinstan for decades to come, as it does elsewhere.
Instead, President Joe Biden took the catastrophic decision to withdraw, finishing a process started by his predecessor Donald Trump. In truth, Mr Biden was never keen on US involvement in Afghanistan and his views as vice-president were at odds with many in the Barack Obama administration.
But after 20 years of "nation building", Mr Biden's antipathy towards the mission had gained significant traction with the US electorate. When the withdrawal came the Taliban wasted no time in reasserting themselves. There are reports of summary executions, children being recruited as soldiers and prisons being emptied. Women and girls have had their right to education stolen from them.
It seems there is a squeamishness about intervention. Why should we in the West see ourselves as the arbitrators of right and wrong? But we should not wring our hands about intervening in such circumstances. If we are in a position to right wrongs we should feel no compunction about doing so.
The consequences of this reluctance to stand up for basic human rights are being played out in Kabul. The Western alliance could have found a middle ground betwen all in and all out. The shameful failure to do so has diminished the West as a force for good in the world and the Afghan people will suffer the consequences for decades to come.