A detailed analysis of the fall of Afghanistan suggests that the Pentagon and presidents Trump and Biden had plenty of warning that the Afghan armed forces would quickly buckle without America’s support and that the war would end with the Taliban in control of the country again.

Assigned by Congress, the interim report by the Special Inspector General for Afghanistan Reconstruction says that, despite $90 billion in aid over two decades, the Afghan National Defense and Security Forces were nowhere near ready to take on the Taliban by themselves when in early 2021 Mr. Biden reiterated Mr. Trump’s promise to withdraw all American military forces and contractors. The country’s implosion, the report says, was as predictable as it was rapid.

“After 20 years of training and development, the ANDSF never became a cohesive, substantive force capable of operating on its own,” the report concludes. “The U.S. and Afghan governments share in the blame. Neither side appeared to have the political commitment to doing what it would take to address the challenges, including devoting the time and resources necessary to develop a professional ANDSF, a multi-generational process.”

The report offers a blistering assessment of America’s efforts to extricate itself from its longest armed conflict and the Pentagon’s attempts to build a modern army from scratch. The February 2020 decision by the Trump administration to commit to a rapid withdrawal sealed the fates of both the ANDSF and the country, the report’s authors conclude.

“Many Afghans thought the U.S.-Taliban agreement was an act of bad faith and a signal that the U.S. was handing over Afghanistan to the enemy as it rushed to exit the country; its immediate effect was a dramatic loss in ANDSF morale,” the report says.

Early in his administration, Mr. Trump ramped up military involvement in the nation, dispatching an additional Army brigade, deploying a GBU-43 Massive Ordinance Air Blast — better known as the Mother of All Bombs — on ISIS positions in the country, and increasing the number of airstrikes on Taliban positions. During 2019, America launched more than 7,400 airstrikes against Taliban positions — the most since 2009.

Then everything came to a screeching halt. In February 2020, the Trump administration signed a deal promising to withdraw all military forces and contractors from the country in exchange for Taliban promises not to attack American and allied forces. The government of Afghanistan was not involved in those negotiations. Within months, Taliban forces launched a major offensive against the Afghan army.

In March 2021, the Taliban warned the new Biden administration that attacks against U.S. forces would resume unless America stuck to its promise of a complete withdrawal by May 1. Mr. Biden hesitated, but later promised that everyone would be gone by September 11, 2021, the anniversary of the attacks that precipitated the war.

By late August 2021, however, the point was moot. The Taliban had already captured 33 of Afghanistan’s 34 provinces. On August 15, they arrived at the gates of Kabul and President Ashraf Ghani fled to Uzbekistan. By then, six of the seven Afghan Army corps had already surrendered. On August 30, the last U.S. troops left the country.

Congress created SIGAR in 2008 to provide independent assessment of efforts to rebuild the country following the 2001 invasion. The latest report is based on interviews with more than 40 Afghan and American officials as well as hundreds of government and academic reports on the $140 billion in U.S. aid that has poured into the country since 2002.

SIGAR says that despite the 600,000 weapons, 300 aircraft, and 80,000 vehicles donated by America to the Afghan defense forces — some of which are now being used by the Taliban, both in the field and for propaganda purposes — much of the Afghan army crumbled within weeks of the Taliban gaining the upper hand in August 2021.

Much of the materiel given to the Afghans was sophisticated weaponry requiring regular maintenance and training to use, and was all but useless with U.S. soldiers and contractors gone. President Ghani compounded the problem by replacing young, professional soldiers and officers trained by the United States with political cronies, the report says.

Egged on by politicians in Washington eager for an exit, the American military mistakenly used battlefield wins as the primary metric of success. Because the Afghan forces were sub-par, achieving those metrics often required American forces to step to the forefront in engagements, leaving Afghan troops to serve as what a retired general, David Barno, called “window dressing” for many missions. Consequently, many Afghan soldiers never gained the experience necessary to fight for themselves.

SIGAR says there were warnings about the viability of the Afghan army as far back as 2014. In testimony before the Senate Armed Services committee that year, General Joseph Dunford, then the top commander in Afghanistan, warned that once coalition forces withdrew, the Afghan security forces “will begin to deteriorate … I think the only debate is the pace of that deterioration.”

Pentagon planners also erred in attempting to create in the Afghan forces a mirror-image of America’s professional army, such as forming a cadre of non-commissioned officers where none had existed before. The Afghan Air Force was created with the full knowledge that it would not be self-sufficient until at least 2030, the report says.

The tone-deaf attempts to impose a foreign culture on the Afghan army “created a combined arms military structure that required a high degree of professional military sophistication and leadership,” the report’s authors concluded, neither of which existed in the nascent Afghan military.

In its conclusion, the report notes that America has attempted to build armies in other countries four times in the past 72 years, and three of those — Vietnam, Iraq, and Afghanistan — have been “catastrophic failures.” Only South Korea, which took seven decades and still costs $3 billion a year, was relatively successful.

Behind those failures, the report said, is the mistaken assumption that “superpower ways of waging war can be transplanted to smaller, poorer countries without factoring in the political or cultural context in which those armies operate, or adapting our methods to the means at hand.”

This week’s report was described as interim, with the full findings coming later this year. The complete report is available on SIGAR’s website.