"The imminent fall of Afghanistan is more than a national disaster. It is not just that the gains made in the past two decades, at the cost of tens of thousands of lives and trillions of dollars, look certain to be reversed as the Taliban advances," Greg Barton wrote in an opinion piece published in Asia Times.

"The Taliban’s victory is also al-Qaeda’s victory, and it has global implications," Greg Barton wrote.

"Even before the US military completes the final steps of its troop withdrawal, the Taliban are surging. They are now reported to control 212 districts – more than half of Afghanistan’s 407 districts. This is triple the territory it controlled on May 1. The Taliban have seized 51 districts since the start of July alone," the writer said.

The Taliban are currently busy fighting to take control in further 119 districts.

The government will be left with the control over only 20 percent of regions in the country.

"Afghanistan was the birthplace of al-Qaeda in 1988. The group gave rise to terrorist networks around the world, including Southeast Asia’s Jemaah Islamiyah, formed in Afghanistan in 1993, and Al Qaeda in Iraq, which morphed into the Islamic State in Iraq in 2006," the writer said.

"A Taliban-controlled Afghanistan – a return of the Islamic Emirate of Afghanistan – will be much larger and prove much more durable than the ISIS caliphate in Syria and Iraq could ever have been. This will be a powerful inspiration for jihadi terrorists everywhere," the expert said.