September 1 was the first, day of school in the sleepy North Ossetian town of Beslan, when parents, teachers and children celebrate The Day of Knowledge’ by wearing their best clothes and school uniforms. Instead of a party with music and dancing, they stepped into a brutal nightmare. Clubbed and beaten into the school gym by Chechen militants, more than 1,200 civilians found themselves at the mercy of gun-toting fanatics prepared to abuse, torture, maim and kill them in pursuit of concessions from the Russian government, their ‘oppressors’. In the convoluted morality that guided competing territorial claims in the Caucasus (Russia, Chechnya, Ingushetia and North Ossetia could not even agree a rationale for their bitter confrontations), the hostages were to be expendable human pawns.

The screams and chaos that accompanied the initial shooting quickly settled into the groans of the wounded and whimpering of children denied water, food and the lavatory. The toxic sweat of fear mingled with vomit and rotting corpses. The militants had moved swiftly to wire the school with explosives, and several were living grenades – suicide bombers anxious to make their mark with the world looking on and Russian Special Forces among the thousands of surrounding troops. Handfuls of hostages escaped, but catastrophe was inevitable.

After 51 hours, Russian assault troops rushed the school using tanks, rocket-propelled grenades, flame throwers, helicopter gunships and anti-personnel high explosives. As whole sections of wall collapsed on some of the hostages, bombs were triggered, and the school erupted. Explosions continued throughout a 12-hour gunfight, in which hostages were shot indiscriminately by their ‘rescuers’. With no fire crews and few ambulances to help, bystanders braved the inferno to get some of the hundreds of injured hostages to safety in private cars; 334 of their friends, neighbors and children were already dead.

When: September 1-3 1994

Where: Beslan, North Ossetia

Death toll: At least 334 died, including 186 children. Most of the militants were also killed, and it’s not clear if they or the many injured who died in hospital are included in that total (because the Russian government conducted at least one mass burial of more than 125 people). Many other hostages ‘survived’ but remain too traumatized to resume their former lives, and several have committed suicide.

You should know: The Beslan massacre was a manufactured crisis intended to aggravate the great powers rather than to achieve a local objective. Behind every sobbing Beslan mother is the cynical and underhand power politics of governments.

As the millennium loomed, Christianity in Africa blossomed to equal or surpass the number of its European adherents. African Christians are especially attracted by charismatic offshoots of the Catholic and Anglican creeds, and Uganda’s traditional culture of obedience, respect and loyalty makes it unusually fruitful for new sects. The more exciting, the better. Hoping to find what the executive secretary of the Uganda Joint Christian Council described as ‘easy answers to the difficult questions’, there were plenty of eager takers for the strong spiritual leadership offered by Credonia Mwerinde, founder of the apocalyptic sect called The Movement for the Restoration of the Ten Commandments of God.

Mwerinde presented herself as a redeemed Mary Magdalene who had turned away from sin after ‘a vision of the Virgin Mary’ and was therefore fit to dictate terms on other people’s waywardness. With a talented preacher as partner, she built up a dedicated following in southwest Uganda. Rules were strict: separation of families, celibacy, absolute silence, obedience and commitment to a millennial ‘rapture’. This last was conditional on donating all your worldly goods to Mwerinde.

Having prepared her followers for the millennium, Mwerinde had to explain why the world hadn’t ended. She blamed it on their concealed ‘sins’ and quickly re-scheduled for March 16. On that night, she locked them in their prayer hall and set them on fire.

The fireball killed at least 330, but it was just the beginning. Across southwest Uganda, a series of mass graves revealed more than 700 bodies, stabbed, strangled and burned. Very probably there are more still. The cult’s leaders were not among them – they were last seen driving north with suitcases full of valuables.

The heart-breaking credulity of their victims, up to the last minute of horrified disillusion, stripped the crime of any pretension to religious suicide. This was mass murder at its ugliest, and was without doubt planned ‘with malice aforethought’.

When: March 16-17 2000

Where: Kanungu, Uganda

Death toll: 330 at Kanungu (the police clearing the ashes believed it could be as many as 550), with a further 725 or so recovered from several locations. The dead included a number of children.

You should know: Indoctrinated cult members were given an extended ‘home leave’ in 1998. The dates coincided with the treatment for bipolar disorder and manic depression, in a Kampala mental hospital, of Joseph Kibwetere, the preacher who was Mwerinde’s accomplice. There’s a price on his head for murder.

The Columbine massacre was one of the deadliest school shootings in US history, its circumstances and aftermath inflicting untold trauma on American culture.

Eric Harris, aged 18, and Dylan Klebold, 17, armed themselves with homemade bombs, sawn-off shotguns, semi-automatic rifles, pistols and knives. Their objective was an all-out assault on the Columbine

High School in the suburban town of Littleton, outside Denver. They planned a diversionary explosion to draw off emergency services, then they would explode two more bombs inside the school and pick off survivors as they ran. Their intention was to kill hundreds of people, dwarfing the Oklahoma City carnage with an obscene disaster that would forever besmirch American history.

When the two interior bombs fizzled but failed, they swaggered through the school shooting at anything and anyone. It was fun, especially in the packed cafeteria where their terrified peers shrank under the tables hoping to escape notice and make a break for it.

It’s taken a decade of deconstruction for the police, FBI, survivors, victims’ families, public and Michael Moore (who made the seminal film Bowling for Columbine) to reach any kind of cogent explanation for the murders. Prolonged study of video and notebook diaries show that Harris and Klebold had spent a year planning this major atrocity in detail. Columbine School was merely convenient.

They weren’t even seeking fame, they just wanted to hurt as many people as possible. Harris was a clinical psychopath and Klebold a troubled adolescent with a suicidal tendency.

The true, almost unspeakable, horror of the Columbine massacre is that, had the boys been older with greater technical knowledge, they would have committed a far deadlier crime. On the front page of his journal, Harris had scrawled: I hate the f*****g world’.

When: April 20 1999

Where: Columbine High School, Littleton, Jefferson County, Colorado, USA

Death toll: 13 (12 students and one teacher) dead; 23 injured.

You should know: Repercussions of the massacre continue. America watched the siege unfold on live TV, and the subsequent national debates cover access to guns, school security systems, violence on TV and in video games, and police ‘procedures’ (the sensitive issues of why the police failed to enter the school and shoot the two boys; and why they left a teacher to bleed to death on TV; and whether the job of a policeman includes taking risks). ‘Columbine’ has entered American vocabulary in all u kinds of contexts, and none of them are pleasant.

In March 1997 in a house in California police found 39 bodies lying neatly in their bunk beds, their heads and torsos covered by purple cloths. All were wearing black shirts and trousers; in their pockets they each had a $5 note and three quarter coins; each had an armband patch reading ‘Heaven’s Gate Away Team’. They had all drunk a cocktail of vodka and phenobarbital and wrapped their heads in polythene bags.

Heaven’s Gate was one of many millennial and UFO-based cults in the USA. It was originally set up in the early 1970s by Marshall Applewhite together with Bonnie Nettles, who died in 1985. They were known as ‘Do’ and ‘Ti’ and believed themselves to be ‘The Two’ (two ‘witnesses’ mentioned in the Book of Revelation). The cult combined various beliefs – Christian salvation and apocalypse, evolutionary advancement and travel to other worlds. Members renounced family and worldly goods to live a communal life of asceticism and celibacy in a rented mansion they described as a monastery. They called each other brothers and sisters and knew that the next level of existence would be free from gender and sexual activity – some, including Applewhite, underwent castration.

Central to their faith was the idea that the earth, controlled by evil powers, was about to be ‘recycled’ and that they must leave it immediately, to be ready for ‘replanting’ in another container (body) at a higher level. A video shot just before the suicides shows cult members thrilled by the prospect of joining a UFO hidden behind the Halle-Bopp comet, which they regarded as a celestial marker. They had timed their departure to coincide with the comet’s closest approach to earth.

When: March 26 1997

Where: Rancho Santa Fe, near San Diego, California, USA

Death toll: 39 (plus two cult members who killed themselves later)

You should know: When contacted early in March about taking part in Louis Theroux’s weird Weekends series, Heaven’s Gate refused the invitation, saying it ‘would be an interference with what we must focus on’.

There were 29 small children in the gymnasium of Dunblane Primary School when Thomas Hamilton walked in and opened fire at point-blank range. Using several automatic firearms, he sprayed and re-sprayed the room. In just three minutes 16 children were dead or dying along with their teacher, and 12 were wounded. Just one of the five and six year olds escaped the carnage physically unscathed. Then, without pausing, Hamilton shot himself. It was the worst multiple murder Britain had ever known.

Hamilton’s dogged focus on young children as his victims made the Dunblane massacre even more horrific than Hungerford, nine years earlier. Michael Ryan, the Hungerford killer, had been deemed a fantasist whose violence had been nourished by a lifetime of voluntary isolation from normal societal interchange. As police and psychologists desperately sought to identify Hamilton’s motivation – if only to help grief-ravaged parents make some sense of the horror – it became clear that Hamilton had been isolated. Facts about him included being rejected as a suitable leader of all manner of boys’ clubs, including the Boy Scouts, over a number of years; and he certainly had a clinical ‘persecution complex’, evidenced by his dozens of complaints to councils, parliament, the police, the Ombudsman and even the Queen about his mental stability being questioned. Yet his firearms license was not revoked, and afterwards his keen membership of a gun club was interpreted as a ‘behavioral tryout’.

Finally, he was rejected as a voluntary worker by the Dunblane Primary School. After a lifetime trying to belong to the community, his awful, bloody revenge was symbolic. Instead of the adult authorities who had systematically excluded him – without ever, once, offering him any kind of counselling for his perceived and stated shortcomings – Hamilton attacked those they held most dear, their children.

When: March 13 1996

Where: Dunblane Primary School, Dunblane, Scotland, UK

Death toll: 17 (16 children and their teacher), plus 12 wounded

You should know: After talking to witnesses who saw Hamilton cross the school playground, push past two staff members in a corridor, and pass the dining room before entering the gym, a senior forensic psychiatrist stated that Hamilton’s primary motive was suicide, and that ‘it was not my impression that he particularly relished the killing spree or wanted to prolong it’. We don’t need to forgive Hamilton, but we do need to understand that if we ostracize the ‘weird’ and ‘suspicious’, and ignore their complaints about it, we shouldn’t be surprised if they eventually do terrible things.

The euphoria of independence didn’t last long in most Balkan countries. As the former Yugoslavia fragmented, age-old sectarian, ethnic and tribal rivalries were revived. In 1993 UN forces called in to buffer the antagonism between Bosnian Serbs and Bosnian Muslims had designated several ‘Safe Areas’ for civilians. One of these was Srebrenica. By July 1995, as Bosnian Serb forces laid siege to the enclave, Srebrenica was crammed with Muslims under the protection of 600 UN Dutch troops to whom they had surrendered their weapons.

On the afternoon of July 11 Serb commander Ratko Mladic, having humbugged the UN peacekeepers, entered Srebrenica like some beaming Goering, festooned with news crews. Fearing the worst, that night 15,000 Muslim men (civilians and unarmed ex-fighters) attempted a mass break out across the hills. They were heavily shelled and many were recaptured. Next day Mladic ordered that all men between the ages of 12 and 77 be held in trucks and warehouses for ‘interrogation for suspected war crimes’; while convoys of buses deported 23,000 women and children to distant ‘Muslim territory’.

The killings had already begun in the village of Kravica when the UN forces in nearby Potocari handed over 5,000 Muslims in their charge to the Serbs in return for 14 Dutch hostages taken earlier. The 2,000 elderly and infirm men were separated, driven away and killed. Under Mladic ‘ethnic cleansing’ quickly became methodical and organized. If they weren’t hunted down in the forests, unarmed men were pushed into warehouses or just lined up and machine-gunned, with a bullet or bayonet in the neck for certainty. Bratunac, near Srebrenica, was one favored killing ground – because Serbs had already used it in 1992 when they tortured 350 Muslims to death. This time the victims had to dig their own graves before being shot; 400 were simply buried alive, bulldozed into the earth. In total 8,000 men and boys died in the genocide. It was the worst atrocity in Europe since World War II.

When: July 11-15 1995

Where: Srebrenica district, Bosnia-Herzegovina

Death toll: 8,000 men and boys. Almost as ugly as the genocide itself was the Serbs’ attempt to cover up their crime. They moved the mass graves and tried to camouflage them. Srebrenica massacre sites are still being discovered – only 3,000 bodies have so far been found.

You should know: A video of Ratko Mladic shows him strutting through Srebrenica on July 11, saying to camera ‘the time has come to take revenge on the Turks’. After it was shown at the trial of Radovan Karadzic (Mladic’s commander-in-chief) in The Hague, Karadzic said his only regret was that ‘some Muslim men got away’. For the rest of the world, bringing the murderers to justice is one thing – learning that membership of the UN carries a very real responsibility to keep its promises is more difficult. The Bosnian Muslims of Srebrenica had been ‘guaranteed’ a safe haven.