When the veteran military historian Professor Michael Howard raves about a book by a little-known, 30-year-old ex-Gurkha officer and declares it to be comparable to Clausewitz, it is surely worth snapping to attention. And after reading War From the Ground Up, I am all the more intrigued to meet its author, Emile Simpson. Drawing on his experience of fighting in Afghanistan, Simpson has written an engrossing account of the 12-year conflict that challenges the way we think about war and suggests how we might better fight the next one. “War From the Ground Up is a work of such importance that it should be compulsory reading at every level in the military,” Howard concluded in his Times Literary Supplement review.

Sitting in the Drapers Arms on a gloriously sunny day in north London, Simpson looks every inch the military man, from his regulation haircut to his civilian uniform of brown sports jacket and green tie. As he rises to greet me, the tall, athletic Simpson exudes an air of orderliness. His voice, modulated by his schooling in Cambridge and the parade grounds of Sandhurst, is one notch too loud, as is often the way with army officers.

We decide to move to the garden of the Islington gastropub, which he says is one of his favourite watering holes. It is eerily deserted on a Friday lunchtime. As we settle at a shady table, I ask Simpson whether he is from a military family and what first drew him to the army. He explains that his parents are both Cambridge academics who were somewhat surprised by his choice of career. “My interest in things military was part through history and [part] a spirit of adventure,” he says, in the slightly elliptical manner he deploys when talking about himself.

On a gap year spent teaching in Nepal, he was drawn to the local culture and traditions of the Gurkha regiment. After studying history at Jesus College, Oxford, where he was tutored and inspired by Niall Ferguson, he went to Sandhurst, where he was commissioned as an officer in the Royal Gurkha Rifles. In his six and a half years in the army, Simpson served three tours in southern Afghanistan, first as a platoon commander in charge of 30 men in Kandahar in 2007, then as a military intelligence officer helping to fight the counterinsurgency in Helmand province in 2010, and, finally, working at headquarters of the International Security Assistance Force (Isaf) under the US commander General John R Allen in 2011. Like Carl von Clausewitz, whose service in the Prussian army during the Napoleonic wars shaped his classic book On War, Simpson’s writings are informed by deep personal experience as well as a fascination with military theory.

Before we can plunge too deeply into Afghanistan, the waitress arrives to take our order from the surprisingly ambitious menu. Simpson goes for steak tartare and Dorset crab. I opt for the smoked mackerel and am also tempted by the crab. We order two glasses of Picpoul.

Simpson says that what intrigued him as a frontline officer was how much his experience on the ground diverged from what he had been taught about war and the way politicians talked about the conflict. Clausewitz still largely defines how most people understand war: it is primarily seen as an interstate activity that is polarised, decisive and finite. One side wins, declares victory and imposes its terms – and narrative – upon the loser. The other side accepts defeat, licks its wounds and works out how to fight smarter next time.

But the Afghanistan conflict, which has lasted longer than the two world wars combined, does not neatly conform to this pattern. Who is the enemy? How do you know when you have won? What would victory even look like? At times, when Simpson was fighting in Helmand at the height of the counterinsurgency, the battle lines were fairly clear. “We were fighting the Taliban pretty much every day. There were a lot of casualties – both ways. The battle group as a whole [of 1,000] had about 110 wounded and 28 dead, both British and Afghans,” he says.

At other times, it became near-impossible to distinguish between enemies and friends. The conflict appeared kaleidoscopic, indecisive and seemingly infinite. In his book, which interweaves military theory with personal anecdote, Simpson cites the example of one local commander who was notionally on the side of the Afghan government in Kabul but “rented” out some of his forces to the local Taliban because they had agreed to pay for them. In such situations, trying to divide the population between “them” and “us” was not only dangerous but counter-productive. “There were not two sides. Everyone was on their own side,” he says.

What frustrated Simpson was that abstract doctrinal concepts kept obstructing sensible operational judgments. “The metrics of success were based on red and blue and geographical control of an area – blue being our own forces and red the enemy,” he says. By 2010 his unit had developed its own alternative metrics “identifying different constituencies in the area you were operating in, be they violently or politically hostile to you, sympathetic or undecided.

“From that understanding, you could use both military means and non-military means, working with our civilian counterparts, to deliver a narrative, or a political story, if you like – just like a politician might deliver a narrative during an election. You give each constituency what it wants while going on the offensive against the opposition’s narrative.”

Simpson is as passionate in talking about army doctrine as he is dispassionate in talking about his own personal experiences. But he uses a very different vocabulary from the normal terms of military discourse – “persuasion”, “opponents” and “strategic audiences” in place of “force”, “enemies” and “targets” – and draws inspiration from sources as varied as Aristotle’s teachings on rhetoric and medieval theologians. As he expounds his theory of “armed politics” with eloquence, I am struck by his more than fleeting resemblance to a young David Cameron.

Our starters arrive and Simpson laughs at my mackerel, an upturned tail of a fish pointing up to the cloudless sky. He tucks into his steak tartare and launches into an explanation of how the relationship between soldiers and politicians must change if we want to fight 21st-century conflicts more effectively.

Simpson says that the accepted model for civil-military relations remains Samuel P Huntington’s classic book The Soldier and The State, first published in 1957. That book’s main reference point was the showdown between President Harry Truman and General Douglas MacArthur during the Korean war when the over-mighty general threatened to unleash nuclear war on China. Huntington argued that generals should never again be allowed to have that level of strategic authority, and that policy guidelines should be set by the president. There was also the longstanding constitutional argument that soldiers should not interfere in setting policy because that was the preserve of elected politicians. While that policy may have made sense during the cold war, it does not convince Simpson today. “What I am saying now is that the constitutional argument still makes sense but the strategic argument doesn’t. What you have now is the politicisation of military action down to a tactical level.”

As Simpson puts it, strategy is always “the dialogue between desire and possibility”. Politicians may desire an outcome but their strategy has to be tempered by the operational realities on the ground. In conflicts such as Afghanistan, those frontline soldiers responsible for implementing armed politics on the ground must have more say in shaping and presenting that strategic narrative. “Huntington’s one-way flow simply does not make sense if you want a nuanced political approach down to the tactical level,” he says.

The crabs arrive accompanied by an array of crushing and gouging instruments that would not have disgraced a medieval dungeon. And, however splendid the crab looks and tastes, I quickly realise it was the daftest main course I could have ordered. Extracting meat from a crustacean’s extremities is not compatible with taking shorthand notes. While we’ve been talking, the pub garden has slowly filled up with fashionable young mothers and prams. The badlands of Afghanistan could not seem further away. I ask him what he thinks will happen when Nato forces pull out next year.

As he rips a claw off his crab, Simpson says he doesn’t foresee a dramatic collapse of the Kabul regime. The government’s endemic corruption poses a bigger threat to its survival than the Taliban does, he argues. When Soviet forces withdrew from Afghanistan in 1989 they left behind a reasonably stable regime that was still able to defeat the Mujahideen when they massed for a conventional battle at Jalalabad later that year. It was the implosion of the Soviet Union in 1991 that doomed the Najibullah regime by cutting off its funding. The regime in Kabul today may not be very democratic or effective, he says, but it is unlikely to be overthrown by force.

“The Taliban can take dusty villages but for them to present an existential threat to the state means they have to knock out the Afghan army backed by US air power. They did not do it with the Russians. They will not do it today. If the state fails, it will be because it implodes as a result of corruption,” he says. As fragments of dismembered crab are cleared away from the table (and my notebook), Simpson orders a lemon tart and I plump for a poached pear. I am keen to prolong the conversation and explore one of the other big ideas of his book: the fact that social media has had a transformational effect on war.

Unsurprisingly, we return to Clausewitz, who is still taught in military academies today. Simpson rejects any suggestion that his work is comparable. “That would be incredibly immodest and inappropriate,” he says. “But my book is an interpretation of Clausewitz in the modern day …[On War] is characterised by dialectics, between theory and experience, between history and the present day, between intuition and doctrine …It is very much located in reality, but not consumed by it. I very much identified with that experience.”

As a young soldier in the Prussian army, Clausewitz fought at a time when the whole conception of conflict was being revolutionised. In the late 18th century, war was not unlimited: the great powers would try to defeat the enemy on the battlefield to gain an advantage but they rarely knocked out other states. Following the French Revolution, Napoleon was able to mobilise millions of soldiers and overthrow other regimes. “The whole state was at risk. It was a fundamentally different concept,” Simpson says.

He argues that a similarly decisive change in conflict is taking place today. Thanks to videos taken on smartphones and the universality of social media, the “strategic audiences” in any war are global. As we are seeing in Syria, images of conflict can be flashed around the world in a heartbeat. “Can we get back to a situation where there is a clear divide between military and political activity? I don’t think we can. Any war is going to be contaminated by contact with audiences around the world who have an interest in that conflict,” he says.

That has two big consequences. First, there needs to be a fusion of military and political activity at the operational level. But, second, conflicts have to be dealt with on their own terms and compartmentalised to prevent their proliferation, as the French have successfully done in Mali. “How you can box in a conflict will be the number one strategic question that will govern the next few decades,” he says.

In Simpson’s view, one of the biggest mistakes the US has made has been to talk about a “global war on terror”, a phrase he describes as silly because it raises expectations that can never be met. “If you elevate this to a global concept, to the level of grand strategy, that is profoundly dangerous,” he says. “If you want stability in the world you have to have clear strategic boundaries that seek to compartmentalise conflicts, and not aggregate them. The reason is that if you don’t box in your conflicts with clear strategic boundaries, chronological, conceptual, geographical, legal, then you experience a proliferation of violence.”

Simpson finished his last tour of Afghanistan just before Christmas 2011 and left the army shortly afterwards because it “was mainly incompatible with personal life, my girlfriend and my family”. He also had broader frustrations with the career structure in the army. “If you are a reformist and want to reform the army then you have to bide your time, as you do in any organisation. Just being in a bureaucracy in general was quite frustrating,” he says.

Simpson has switched careers and is now studying international law, a field in which he hopes he can combine both theory and practice. But he will not be wholly lost to the field of military doctrine as he is already working on another book about the concept of the enemy. His spirit of adventure is sated by trekking trips in Nepal and cycling tours in Oman.

Since his book’s publication in 2012, Simpson has been invited to speak to several military audiences in the US, where the debate still rages about how best to conduct counterinsurgency campaigns. It has received a cooler response from Britain’s top brass, despite Professor Howard’s endorsement, but Simpson says the army is slowly becoming more receptive to fresh thinking because of its recent setbacks in Basra and Helmand.

“Thirty years ago, if you could drink a bottle of whisky in the evening and run 10 miles in the morning and had a big moustache, then you were a good bloke and didn’t need to read anything. But today the army is much more open to reading. The army has got less afraid of intellectualism since things went wrong in Iraq and Afghanistan,” he says. “We do need to rethink our profession.”

John Thornhill is the FT’s deputy editor

——————————————-

Drapers Arms

44 Barnsbury Street, London

2 glasses Picpoul £11.50

1 steak tartare £7.50

1 smoked mackerel £6.50

2 Dorset crab £27.00

1 chips £3.50

1 potatoes £3.50

1 lemon tart £6.50

1 poached pear £6.50

Total £72.50