evidence: After the final withdrawal of US troops from Afghanistan, President Biden suggested that the war in Afghanistan had most likely cost the USA more than US$2 trillion. While most of the estimated expenditure was on US military operations, the USA also devoted substantial financial resources to reconstruction activities. [...] Afghan military expenditure in the period was only a fraction of total US military aid to Afghanistan. Between 2004 and 2020, the Afghan government’s military expenditure totalled $3.7 billion in current dollars or $3.6 billion in constant 2019 dollars, equivalent to only 4.6 per cent of all US military aid disbursed to Afghanistan. Afghanistan’s average annual spending in 2004–20 was $219 million and, in constant 2019 dollars, never exceeded $270 million in any of the 17 years for which data is available (see figure 3). [...] Two key issues stand out after the withdrawal of US and allied forces from Afghanistan and the subsequent rapid defeat of the Afghan military. The first is the future of the Afghan military under a new Taliban government. Much has already been written about the capacity for Afghanistan to generate sustainable revenue to support its public expenditure. The affordability of the Afghan military over the past two decades—irrespective of its effectiveness—was dependent on US support. With the end of US military aid, what will happen to the Afghan military as an institution and how will it be funded? China, Russia and Turkey are a few countries that observers mention as being prepared to replace the void left by the USA and its allies.