When he was a boy, in the 1970s, Srdja Popovic used to crawl through a hole in the wall of a half-built cathedral. “It was my playground,” he says. We are in downtown Belgrade, and Popovic is talking about his work, his city and, for now, the vast white building in front of us, the Cathedral of St Sava.

He was nine, a new recruit to the international army of “Lord of the Rings” fans. He made the north tower his own, naming it Barad-dûr after Sauron’s fortress in Mordor. He was old enough to know that Nazi bombing (in 1941) had halted the construction of the cathedral (begun in 1935), young enough not to be aware of any danger. For him and his friends, the surviving shell of walls and towers was a haven. “We used to swap shifts with amorous couples, we took the day shift and they appeared in the evening. We respected each other.”

When politics allowed building to resume in 1985, Popovic’s playground grew into one of the world’s ten largest churches. It can take 10,000 worshippers, but is still unfinished. For the adult Popovic, it is less about Tolkien and more about Serbian history. The church, he tells me, stands on the site where the Ottomans burned the remains of St Sava in 1595. The saint, a 13th-century prince, was the founder of the self-governing Serbian Orthodox church and the author of Serbia’s first constitution. When the Serbs revolted against the Ottomans, his image appeared on the flags they carried into battle. Hence the conflagration of his remains: a pointed retaliation.

Popovic knows about symbols, revolts and rallies. Now aged 39, he was only 18 when he took his first steps as a revolutionary. He was a key member of Otpor (Resistance), the nonviolent, 70,000-strong youth group that helped topple Serbia’s dictator, Slobodan Milosevic, in October 2000. Three years later, he and another Otpor member, Slobodan Djinovic, founded an NGO, the Centre for Applied NonViolent Action and Strategies or, more palatably, Canvas.

Canvas trains pro-democracy activists in lessons derived from Otpor’s experience. And it has impact. Popovic is widely seen as one of the architects of the Arab spring: when the American journal Foreign Policy named its top hundred global thinkers in December 2011, it put “the Arab revolutionaries” at number one, and named Popovic as one of them. He is even, according to the director of the Peace Research Institute Oslo, in line for a Nobel peace prize nomination.

When a repressive regime wobbles, the hand of Canvas can often be seen at work. Ahead of the Arab spring, it trained activists from Tunisia, Lebanon and Egypt. The protests in Tahrir Square, Cairo, that brought down President Mubarak in February 2011 unfolded like something from the Canvas training manual. Among the leaders were members of the April 6 Youth Movement, who had travelled to Belgrade in 2009 to learn how to conduct peaceful demonstrations, and cope with violence from security forces without resorting to it themselves. Canvas also helped them with organisation, mobilisation, overcoming fear and passivity, and training other protesters to spread the techniques.

Popovic is quick to state that the Arab spring is indigenous. “It’s the result of the efforts and perseverance of the brave individuals in each movement. If Canvas’s movies, books and the Otpor symbol have helped, that makes us proud, but we don’t claim any credit. Canvas may have equipped activists from the Middle East and elsewhere with the tools to wage their struggle more efficiently, but it is their victory. It belongs to them.”

The movie he is referring to is Steve York’s documentary about the fall of Milosevic, “Bringing Down a Dictator”, first shown on PBS in 2002. The symbol is Otpor’s clenched fist, designed by Popovic’s best friend, Nenad Petrovic-Duda, and based on the hand of Saruman from “Lord of the Rings”. Canvas’s logo takes the fist a stage further, embedding it in the arrow triangle that is the international symbol of recycling.

When Popovic got married, last summer, Petrovic-Duda was best man. The wedding was a sweltering affair in a glade in a Belgrade park. His bride, Masha, a radio and television journalist, appeared through the trees dressed in white embroidered satin, as the elf queen Galadriel. The groom, by contrast, wore frayed jeans and white sneakers.

Popovic is wearing jeans and sneakers now, at work. His day begins at 8am in a small grey cube of an office in New Belgrade. He is all energy, circling the room. He takes an emergency call from Syrian activists, speaking in Serbian. A response is needed on the Maldives. Other, more secret enquiries, follow. He reverts to English and mentions an American historian, Howard Zinn. “You know what he said?” he asks with a grin. “Education may and should be dangerous.”

With the Arab spring, the nonviolent strategies in which he educates clients have leapt into the limelight. Canvas has been involved in revolutions in Georgia, Ukraine and the Maldives, and works with activists from 40 more countries, ranging from Soviet throwbacks (Belarus) to Asian giants (India and China), Middle Eastern oligarchies (Iran, Yemen) and small, brutal dictatorships (Zimbabwe, Burma).

“Canvas is unique,” Popovic says. “In evolutionary strategy some species accommodate to their conditions…” He looks outside at the grey Belgrade tower blocks. “Like pigeons—they’re everywhere.” Others go for narrow specialisation. “Canvas is like those bacteria that can live at temperatures of 60°C—highly specialised.”

Unique, specialised and, until recently, reluctant to be observed. Canvas “came out of the closet”, as Popovic puts it, by way of an Al Jazeera documentary during the Arab spring (on YouTube). It’s sensitive work. Canvas has been accused of being a tool of Western secret services. “There’s a naive narrative in which these revolutions are a product of Langley or MI6,” Popovic scoffs. “As if all you need is a wad of CIA dollars, a bunch of crazy Serbs, send them to country X and boom, you have your revolution!” He laughs. “If it was a question of money only…”

Canvas’s curriculum, designed to be taken anywhere and adapted to any situation, shows how much planning goes into revolution. “We’re constantly updating, building on lessons learned.” He breaks off to describe a workshop. “One night back in 2006, we were on the beach in Sri Lanka, working long sessions with Maldivian activists. Instead of using flipcharts we were writing in the sand—only to discover that the sand was populated by newly hatching turtles. We had to help them find their way to the sea or they’d have followed the streetlights instead of the moon and been killed on the road. The session turned into a Discovery Channel type of ‘saving baby turtles’ experience—the craziest thing that has ever happened to a workshop.”

More typically, workshops run for five to seven days, with up to 20 activists in the room. “We don’t really give specific advice, but prefer people to develop their own tools—helping them to shape their own indigenous ideas. Normally, they finish the workshop with their own campaign plans and ‘people-power toolbox’ to use once they get back to their organisations.”

The trainers, all former participants in protests, deliver the curriculum, usually in English. The trainees analyse and evaluate their country’s situation, after being coached in the theory of nonviolent struggle and the three principles for its success: unity, planning and nonviolent discipline. They study the role of consent and obedience, and “pillars of society” (military, police, judiciary, bureaucracy), and how to lure ordinary people away from them and towards the nonviolent movement. Next come strategy and tactics, especially “low-risk tactics”, such as co-ordinated banging of metal pans at set times across a city—actions in which all can join, and which keep people in the movement even under harsh oppression.

They focus on communications (targeted and channelled appropriately). They are taught the importance of humour: decorating a barrel, say, with a dictator’s face, encouraging passers-by to bash it, and leaving police with a tricky choice—do nothing and look weak, or confiscate the barrel and look foolish. They are shown how to deal with fear. Having identified the pillars of their particular nation, participants design plans to win them over. “In other words, we give them a fishing rod and teach them how to use it, but the rest is up to them.” The funny thing, Popovic claims, “is that every workshop starts with at least one smart activist saying, ‘Well guys, congratulations, we all know about Otpor…Maybe this worked in Serbia, but it will never work in our country.’ That’s how they begin, and we try to see that they finish day five with a clear idea of what may well work for civil mobilisation in their own society. And the best part is that they reach this answer themselves.”

Popovic was particularly impressed by one of the Egyptian April 6 leaders, Mohammed Adel. “He was with us in Belgrade in 2010. I asked him why they chose the name ‘April 6’ [the date of the workers’ demonstrations in Mahalla in 2008] and he told me, ‘because we understood that we were picking the wrong social space. When we demonstrated for political change in Egypt, we were arrested and tear-gassed all the time. Labour movements protest about bread-and-butter issues and get concessions from the government. We wanted to choose the right battles—the ones we can win, as the labour movement does, and so we picked the name that reflects this.’ A year and half after that, they were winning.”

Successful movements don’t take on unwinnable battles, they opt for small victories and build on them, and they need a strong brand to attract broad support. Clever slogans, unifying songs and identity symbols are vital: Otpor’s clenched fist has been so successful that it is often co-opted by activists with no link to Canvas. “Once I saw it on the T-shirts of a Kenyan group,” Popovic says, “complete with the logo in Cyrillic, which none of them would understand.”

Overcoming fear is a challenge he relishes. “Milosevic played the cheap card of nationalism, using fear to manipulate the population.” Otpor’s experience produced a number of tools for dealing with fear in case of arrest. “We trained activists in what the procedure would be, how the interrogation room would look, how one interrogator would be gentle and sympathetic, the other a bully. Knowing what to expect diminished the fear,” says Popovic. Coded messages were used to set off a list of rapid responses: “Grandmothers who would telephone the police station where activists were held, visitors asking after the arrested, enquiries by international groups, journalists alerted. All to put pressure on the security forces.”

Canvas argues that it’s essential to keep violence out, because one slip will ruin everything. “Here in Serbia”, Popovic says, “we had to spend months persuading the football-fan element to keep out.” Students receive training in techniques to avoid and face violence, especially from the police and the army, without retaliating in kind. “At Otpor we created a party atmosphere, with whistles, drummers, humour—kids having fun. And we used our own security people to be sure the football fans were kept out.”

The Canvas message spreads. Its handbook for activists, “Nonviolent Struggle—50 Crucial Points”, is available in six languages, including Arabic and Farsi, and has been downloaded 20,000 times in the Middle East, largely by Iranians. Its foreign clients are usually young and can identify with Canvas, a small, committed group, born between 1968 and 1975. They are old enough to remember the Tito era of summer holidays on the Adriatic and winter holidays in the mountains near Kosovo, when Yugoslav passports were the most powerful and the most expensive on the black market because “they could get you anywhere, from Washington to the Kremlin,” as Popovic says. “So there we were, aged 18 or 19, ready to be conscripted, to do what? Kill the guys we’d been on holiday with? Faced with this, one-third of us took to drugs and went crazy, a third took off altogether—the biggest brain drain you can imagine—and a third stood up to fight.”

Popovic comes from a liberal, educated home, the son of two respected television journalists. He was influenced by his experiences as a teenager in Belgrade. “We were closely aligned with India and of course Gandhi—his story is so powerful, anti-colonial. His tactics were brilliant.” In 1991, when protests here led to two deaths in one day and the government’s response was martial law, tanks, refugees, uniforms and war in the Balkans, “our response wasn’t so much ethical, let alone religious, it was spontaneous revulsion.” Those protests, for him and other young urban middle-class Serbs, were a landmark. “It was our ‘losing our virginity’—heady stuff, but not very effective.”

He was anti-violence, or as he would call it pro-nonviolence, from an early stage. “Eighteen was the perfect age to be shaped. These crazy romantic guys in rock groups organised the last attempt to prevent war.” A concert in Republic Square was banned, so the protesters put on a moving concert on the back of a truck. The song “Mir, Brate, Mir” (“Peace, Brother, Peace”) rang out time and again. “It was like ‘Give Peace a Chance’, but cool,” Popovic says, teasing. They also sang “Under the helmet there is no brain” —“very provocative. And —” now he looks mildly uncomfortable—“when I shoot, I cannot fuck.” It was very rebellious.

In 1998 they formed Otpor, and in 2000 in Budapest they met Gene Sharp. An American professor, now 84, Sharp is another of Foreign Policy’s Arab revolutionaries. He has been a tireless advocate of nonviolent revolution since the 1950s. He helped Otpor with practical issues and structuring their campaigns, and influenced Canvas later in developing a solid academic base. “By now we had a wider framework, 40,000 people involved, and had come up with the anti-Milosevic slogan ‘Gotov je’, ‘he’s finished’.” In the 2000 presidential election, Otpor’s efforts helped produce a record turnout, 72% of the electorate. “And that was Milosevic, finished.”

In Republic Square, buses come and go as Popovic describes what happened here 12 years ago. Sitting on a concrete bollard, he points to a circle of buildings. “There, and there, members of Otpor were posted.” Each spot was a vantage point, with landlines to co-ordinate events and pre-empt either a government blackout of cellphones or an overload on the system. “Thousands of protesters from all over Serbia were converging on Republic Square to shout out their objections to Milosevic. The government forces were met by protesters with smiles, songs and laughter.” They did not oppose the protesters. They responded by standing by and watching; some even joined in. By nightfall, Milosevic had fled.

After another burst of energy, we’re standing at a crossroads in downtown Belgrade, looking at buildings full of holes. NATO bombed Yugoslavia in 1999 for 78 days, night after night, to impose peace in Kosovo, and Belgrade is still peppered with unrepaired bomb damage. As we look up at the gutted buildings, named after battles fought by Serbs in the second world war, Popovic points out one building in particular, and his face darkens.

In 1996, he explains, he had finished his studies as a freshwater biologist and joined the liberal opposition Democratic Party, becoming the youngest member of the Belgrade City Parliament, at 23. By 1998 he was losing his faith in the party, but still believed in its leader, Zoran Djindjic. Another two years later, Djindjic was prime minister, and he appointed Popovic, by now an MP, as an adviser on environmental issues. “I spent three years persuading people to recycle garbage. The state can only do so much—people have to play their part.” In 2003, in the building Popovic is pointing at now, Djindjic was assassinated. “I’ve been blessed to have two idols, Djindjic being one and the rock star Milan Mladenovic the other.” The first song Popovic learned to play on the electric guitar was by The Clash. Then, noting that I’m British, he adds, “you should know all about The Clash, and Joy Division…”

Canvas started as a hobby. In 2002 Zimbabweans, Georgians and Ukrainians were using the Otpor fist and asking for advice. Popovic was surprised by this, but with Djindjic gone and Milosevic safely in The Hague, he saw the chance to quit politics—“my two good life decisions: quitting politics, and quitting smoking, last year”. Meanwhile his comrade in non-arms, Slobodan Djinovic, had started a successful software business. It is this success that provides the bulk of Canvas’s funds. “With journalists for parents, and a rock star for a brother, I know a few tricks about presentation.”

His aim now is to make people power available and mainstream, through education, academic programmes, university courses and talks. “I’d like to shine the light of people-power science on NATO.” Popovic is a visiting scholar at Columbia University, and lectures at Rutgers and Northwestern. When we met, he had just given presentations to students at two British schools, Eton, near Windsor, and Atlantic College in South Wales—gatherings of young people hearing how a man changed his country’s political system when he was not much older than they are. Popovic, who is invariably dressed casually and considers “wearing a tie is a form of slavery”, was riveted by the formality of Eton with its tailcoats and stiff collars. The boys were more interested in what he had to say than what he was wearing. “It was the best talk I have heard in my life,” said one 15-year-old.

It is hard to imagine nonviolent struggle working every time. Doesn’t it just crumble in the midst of armed conflicts or against the most determined regimes? Popovic is undaunted. “No matter how big or small conflict is, it’s about whether or not you can mobilise numbers, and make the majority of the population active against the guy at the top. Nonviolence will work where there’s any vulnerability in the ‘bad guys’. And they are vulnerable.

“The Hitlers or Assads of this world cannot personally collect taxes, torture citizens, shoot into crowds of protesters, operate public transport or fix roads by themselves. They need obedience and co-operation to do so. And if enough people deny obedience and withhold their co-operation—even after credible threats—rulers simply cannot rule.”

With total confidence, he quotes two American scholars, Erica Chenoweth and Maria J. Stephan. In their study, “Why Civil Resistance Works” (2011), they analysed 323 situations from the period 1900-2006, and found that nonviolent campaigns were successful in 53% of cases, whereas violent ones managed only 26%. Academia is important for Popovic not only as support for his arguments for nonviolent protest, but also in propagating the philosophy. To this end, Canvas has designed a master’s degree for the department of political science at the University of Belgrade. It is awaiting certification and Popovic shrugs with irritation at the red tape.

He talks of Syria, and the choice protesters have faced of whether, and when, to call a halt to nonviolence and pick up arms. As we talked, in March, he felt that the best case study for Syria might be South Africa’s anti-apartheid struggle. “It had three phases—a successful initial nonviolent struggle with the freedom charter and the growth of the African National Congress, then years lost in an unsuccessful and costly (in terms of lives) attempt to challenge the apartheid government with a guerrilla movement,” and in the end, winning over an isolated and economically vulnerable government by shifting to non-co-operation (strikes, consumer boycotts) and wielding vast numbers. “If there’s one field where Assad has a tremendous advantage, it’s the field of armed struggle. If there’s one area he’s particularly vulnerable, it’s the economy.”

“In most conflicts,” Popovic argues, “the only arena in which protesters cannot win is the military one.” And yet, so often, what happens? The military option. Syria, he concedes, is a huge test. “Can Assad go further than Mubarak and Ben Ali with even more ruthlessness and readiness to shoot and bomb his own people?” he wonders. As we talk, it certainly looks that way. “And will the international community learn from the Libyan, Kosovar, Afghan and Iraqi cases and refrain from military intervention?”

He concedes that the Arab spring has problems. “And we’ve seen nonviolent victories followed up by stalemate, coups d’etat or even deeper social crises.” He mentions the Cedar revolution of April 2005, when young Lebanese mobilised and kicked out 14,000 Syrian troops after decades of bloody civil war, without a bullet being fired. “But this was followed by political crisis and armed conflict, ending in a Hizbullah-controlled government that’s still in power.”

The sight of Tunisians voting in their first fair elections in almost 30 years was inspiring. “But the Egyptian nonviolent blitzkrieg, now frozen by the generals on one side and Islamic tensions on the other, while the real drivers of Mubarak’s downfall seem to be marginalised…what the hell went wrong?”

His own answer is, “We’re talking about ‘complete’ and ‘incomplete’ revolutions. Getting rid of the bad guy is only the first of three parts of a democratic revolution.” The other two are electing a democratic government, and protecting it. “In 1961, when President Kennedy announced the plan to land a man on the moon, he didn’t say just ‘get a man to the moon’, but specified getting him back to Earth as well. It seems that the operational planning for some of these nonviolent revolutions has been limited to ‘removing the incumbent regimes’. We’ve learned a lot about how nonviolent movements grow and successfully oppose autocratic governments, but we must work on the next steps.”

He denies having any expertise on transition, “but we do point out measures to make the outcome more durable and more likely to end in democracy”. The factors he lists that made Serbia’s transition a reasonable success include reminding the new government that it was accountable to its citizens. “After the elections in 2000, we put up posters all around the country to let the politicians know we were watching them. They showed a bulldozer—a symbol of our revolution—and the caption: ‘Serbia has 4,500 registered bulldozers and almost 7m potential drivers’. Turning a political movement into a watchdog is the best thing you can do after the fight is complete. You need to have a tool to constantly check the elites and not rely entirely on their goodwill.”

Not far from the statues of young men restraining rearing horses in front of parliament is a building where Popovic’s mother used to work. It stands sliced in two, the front half “melted away”, as Popovic puts it, leaving the insides dangling, thanks to a NATO missile. His mother escaped death by a matter of hours. She was the day editor when the TV station was targeted. Thinking of home, and being bombed, brings Popovic onto the Israel-Palestine conflict. “It has such a wide impact.” Several nonviolent attempts to end the Israeli occupation have failed, so far. Popovic is not to be deflected. “Now nonviolence is all the more important. Previously oppressors could deal with nonviolent protest harshly and get away with it. After the Arab spring, the bad year for bad guys, the price of using force skyrocketed.”

One strategy, adopted by the Holy Land Trust, impressed him. A piece of street theatre, a pilgrimage with donkeys echoing Jesus’s entry into Jerusalem on Palm Sunday, managed to get a few hundred yards beyond the perimeter checkpoints. “This is what we call a ‘dilemma action’. What were the police to do—arrest the donkeys?” In the end, the pilgrims were charged with illegally bringing animals into the city. “No one got hurt, no one was prosecuted seriously. And they made their point.”

In the apartment he shares with his wife, reached by a rickety lift that refuses to go back down again, he shows me his photographs on a large TV screen, and his shrine to Tolkien: a shelf of books in English and Serbian, two Ringwraith figures, a map of Middle Earth. A ring on a chain sits to one side. And a miniature execution block and axe? “Oh, that’s Masha’s, she’s fascinated by Anne Boleyn, so I bought her that.”

There are photos of the wedding (he was back at work two days later), the couple’s log-cabin retreat in northern Serbia, their fishing exploits on various European rivers: Popovic looking into the eyes of a vast captured pike (which he then kissed and released, as is his habit), an underwater shot of a carp, and an underwater shot of Masha swimming.

The international community, Popovic believes, can help promote democratic change through nonviolence. How? “By mediation and representing democratic parties abroad,” he says, or by providing a safe internet platform that cannot be infiltrated by police. “It’s being tried in Iran.” Social media and new technology offer huge opportunities. “Footage taken in the Maldives in February was spread that same afternoon to refute the claim that the political events were democratic change. It was a coup.”

Best of all, Popovic says dreamily, would be “to divert even 1% of the millions of dollars” spent by the West on bombing selected dictators into promoting nonviolent movements. “The biggest hope of the Arab spring”, he goes on, “is to understand that this path is a cheap and efficient way to help.” His enthusiasm dims and reality returns: “But it’s a Don Quixote struggle against the war industry. We’re still dominated by the mantra that oppressors will respond only to force.”

By now we have had a hearty Serbian lunch of chicken with beetroot, pork, rakia (Serbian brandy), and Popovic has explained the tradition of “slava”. “We celebrate our family saint’s day once a year.” Friends visit each other on their saints’ days, out of respect. “That’s how we survived 500 years of Turkish rule. Christianity went underground, and slavas held communities together and sustained the faith.”

Popovic’s faith in his work is palpable. “Djindjic, who learnt English at 41 before making a trip to the US, taught me: you stop learning, you stop living.” There is evidence that such learning is happening, but not always for the good. Canvas’s techniques have been studied by oppressors, and social media have been turned into a tool of repression, with tweets and online groups used to trace and arrest activists and demonstrators identified from internet photographs in Iran. In Egypt, a falsified Facebook group claimed victory over Mubarak to persuade protesters to stop; in Sudan, activists’ Facebook accounts were used by the authorities to spread misinformation about protests.

“The Arab spring was all about respect, dignity and the right to work, and the state not delivering.” He muses: “All these movements lie outside the mainstream, like Otpor and like the hobbits on the journey to Mordor. In desperation at the behaviour of ‘adults’ or those in power, the little guys say, ‘I will take the ring’.”

Even if these movements don’t work at first, Popovic believes, the failure will be temporary, the issues will remain: dignity, equality, the stolen futures. “Social justice connects the dots. And the movement for social justice will be long-term, fuelled by governments leaning right. People power and nonviolence are here to stay.”