Douglas Fry is a Fairfax Media writer.

'Were it not for drones, the United States would probably have had to have invade Pakistan.' So declared Dr John Nagl at a public lecture hosted by the ANU Strategic and Defence Studies Centre in Canberra on Tuesday, 13 August.

It's a bold – and alarming – assertion that speaks volumes for the way drones have changed the course of warfare.

Dr Nagl, a retired US Army Lieutenant Colonel who co-authored FM 3-24 Counterinsurgency Field Manual, the doctrine underpinning the radical overhaul of American operations in Iraq after 2006, noted the effectiveness of American drone strikes against al-Qaeda's central leadership in Pakistan. 'Drones have certainly not been an unmitigated good, but they have allowed us not to invade Pakistan, which would have been really bad', he said. 'They've allowed us to essentially eliminate al-Qaeda Central, which is a strategic success for the United States – a fairly extraordinary accomplishment with relatively minor collateral damage and innocent casualties.'

With the increasing frequency of drone strikes in Yemen as the US stepped up efforts against Al Qaeda in the Arabian Peninsula, Dr Nagl said the program would wind down in Pakistan, in part due to a lack of viable targets. 'I think we've done so well in that fight, in fact, that we're now reaching a point of diminishing returns', he said. 'We killed pretty much all of the bad guys that matter.'

While the threat posed by sub-national groups had diminished, Dr Nagl said Pakistan 'will continue to present a threat to the security of the world'.

'Pakistan scares me silly', Dr Nagl said. 'It confronts a number of insurgencies, it has the fastest growing nuclear weapons program in the world, it is the worst proliferator of nuclear technology in the world.' To complicate matters further, Dr Nagl said Pakistan's nuclear facilities are poorly guarded and vulnerable to attack by insurgents, citing a New York Times report by David Sanger. 'I am much more concerned about Pakistani nuclear weapons than I am about the prospect of Iran acquiring nuclear weapons', Dr Nagl said.

Across the border, Dr Nagl believes there is a tarnished silver lining to Western intervention in Afghanistan after 9/11.

'The challenge of succeeding in Afghanistan – which I believe is not just possible but likely by a pretty low level definition of 'success' – is an Afghanistan that does not allow sub-national terror groups to operate inside its borders, and does not present a threat to the West', he said.

It would be vital for Western militaries to maintain a minor physical presence in Afghanistan through counterterrorism operations and advisor programs for Afghan Security Forces (ASF), Dr Nagl said. Most important, however, was that US Congress 'continues to pay the bills' in fostering ASF development. 'When the Soviet Union departed, the Afghan government held. It held for three years', Dr Nagl said. 'It only fell when the Soviet Union dissolved and stopped writing the cheques that had kept the Afghan military funded.' So long as the funding continues, Dr Nagl believes the ASF and central government will hold fast.

'They will stand against the Taliban...and sub-national terror groups will not be able to operate with impunity inside Afghanistan', he said. 'Importantly, we will have intelligence assets and special forces assets able to see into Pakistan, whose sub-national problems make those of Afghanistan pale by comparison.'

Looking to the uprising in Syria, Dr Nagl cautioned against using the Western-assisted regime change in Libya as a benchmark for success in a similar intervention in Syria. 'Airstrikes on Syria would be enormously costly. It would be very difficult. And there's no appetite in the United States, in Britain, in France, and I believe in Australia...for the scope and the scale of the effort that would be required,' he said.

As Syria's internal conflict dragged on, it had become increasingly complex and drawn in more stakeholders, to the point that anti-Assad forces had become dangerously ill-defined as external jihadists took up the call to arms. 'I'm concerned in Syria that we waited too long, and the good guys are dead, and there's no good side to back now, there's no good options there', he said.

Dr Nagl was a proponent of arming and training Syria's rebels in mid-2012, as were several of President Obama's top advisers. 'We now know Secretary of State Clinton, the then Director of Central Intelligence Petraeus, and SECDEF Panetta all supported a train-and-equip mission to the Syrian rebels. The President chose otherwise', he said.

President Obama's caution in deploying US combat forces other than drones was based on the bitter lessons of the Iraq War. 'We planned for toppling Saddam, but literally had no plan for the day after. What comes after Assad? And how long are we willing to occupy Syria, with how many troops, in order to allow that government to get off the ground? And the answer appears to be: we're not.'

Without the will for international intervention, Dr Nagl believes the Syrian civil war could drag on for decades. 'We constrained...American domestic and foreign policy for generations by the mistake of Iraq', he said. 'And I am afraid that the people of Syria are suffering in no small part as a consequence.'

Photo by Flickr user Defence Images.