Finally, finally the over-long, seven year trial of the leaders of the murderous Khmer Rouge leadership of Cambodia, is over. The two defendants, Nuon Chea and Khieu Samphan, were each given a life sentence.

Of the other three that were tried, one, the ex-foreign minister, Ieng Sary died in 2013, one, Ieng Thirith, the wife of Ieng Sary, was too ill with Alzheimer’s to appear and one, Kaing Guek Eav (“Duch”), voluntarily confessed three years ago and was sent to jail for 35 years.

In the twentieth century two massacres of hundreds of thousands people compete for second place after Hitler’s extermination of the Jews, Poles, homosexuals and gypsies. One is Cambodia and the other is Rwanda. But Cambodia, where the deaths were between a million and a half and two million and the executions around 500,000, carried out by Pol Pot and his Khmer Rouge, probably wins this ugly contest.

A week after they took power in 1975 they forced as many as 2 million people living in the capital Phnom Penh to leave the city and work in the countryside. Thousands died during the evacuation. It was carried out in a hurried, ruthless and merciless way, forcing the inhabitants to leave behind all their possessions. Even hospital patients were forced to leave their beds and join the exodus. Children got separated from their parents, many old and sick died on the road and pregnant women gave birth with no professional assistance. The vast majority of doctors and teachers were killed. The pogrom became known as “The Killing Fields”.

The Khmer Rouge believed this was a levelling process that would turn the country into a rural, classless society. They abolished money, free markets, normal schooling, foreign clothing styles, religious practices and traditional culture. Public schools, Buddhist pagodas, mosques, churches, universities, shops and government buildings were shut or turned into prisons, stables, re-education camps and granaries.

There was no public or private transportation, no private property and no non-revolutionary entertainment. People had to wear black costumes, work more than 12 hours a day and be married in mass ceremonies with partners chosen by the party. Showing affection to family members was forbidden. Intellectuals – often singled out because they wore glasses – were executed. If more than three people gathered together to have a conversation they could be accused of being enemies and arrested, even executed.

The Khmer Rouge ruled until 1979 when they were overthrown by the Vietnamese, their neighbours.

The Khmer Rouge then fled westward and re-established their forces in Thai territory, posing as refugees. Relief agencies, including UNICEF, were taken in and fed them, enabling them to fight another day.

The US, still reeling from its defeat in the hands of North Vietnam, acted on the old adage “My enemy’s enemy is my friend”. Under President Jimmy Carter the US in 1979, wanting to punish Vietnam, persuaded the UN to give the Khmer Rouge Cambodia’s seat in the General Assembly. Ironically Carter, who became president in 1977, had said he was making human rights the centre piece of his foreign policy.

From 1979 to 1990 the US recognised the Khmer Rouge as the only legitimate representative of Cambodia. Every Western country voted the same way as the US with the exception of Sweden. The Soviet bloc voted against. (There are cases of a country going unrecognised- as with the US refusing to give diplomatic recognition to Angola in the 1980s. But Western nations wouldn’t even consider that option.)

At the same time many left wing intellectuals and activists in the West also gave them support. They saw them as a clean communist broom sweeping out the old order.

Samantha Power, now the US’s ambassador to the UN, wrote in her book “A Problem From Hell” that she did not find one US official who remembers reading the UN genocide Convention to see if events in Cambodia matched its requirements.

It wasn’t until June 1990 that James Baker, President George H.W. Bush’s Secretary of State, announced a change in policy. Later the Big Five on the Security Council announced that Cambodia would become a UN protectorate. After laborious negotiations the UN finally decided set up a hybrid court with both Cambodian and international judges to put the Khmer Rouge leadership on trial.

It is a good question why the Nuremberg court that tried the Nazi leadership should only take one year and this took seven years. During my visit last year to the court it was the defence lawyers who were dragging it out – but the judges let them.

Yet a sort of belated justice has been done. Fortunately, we now have the International Criminal Court for trying crimes against humanity committed since 2002. It is a much speedier operation, although I would say still not fast enough.