Back in June 1988, 72,000 people crammed into the old Wembley Stadium.
They were treated to a music masterclass. Some of the eighties' best were performing: Simple Minds, Whitney Houston, Stevie Wonder, Sting.
But this wasn't a run-of-the-mill concert. It had been organised by the British Anti-Apartheid Movement as part of its 'Freedom at 70' campaign.
The Wembley concert was kicking-off a month of events leading up to Nelson Mandela's 70th birthday, thirty years ago today on 18th July 1988.
A torrid history with Britain at its center
The African National Congress (ANC) leader had now been a political prisoner of the South African regime for 25 years, and the global movement against Apartheid was turning up the heat for his release.
But the success of the 'Freedom at 70' campaign is the end, not the beginning, of a story – the story of the struggle waged by Britons against the brutal racism and colonialism of faraway South Africa.
For the Jacob Rees-Moggs of Britain, the postwar years were a period of national decline, as the country left its colonies and lost its long-cherished imperial grandeur.
But for us on the Left, this story isn't a sad one. It's the story of a social renaissance, when Britons began at long last to campaign in large numbers against the oppressive empire our country had forced onto the world and its painful legacies.
One of the best parts of this awakening was the Anti-Apartheid Movement (AAM).
It was Britain's Liberal (!) government that had first allowed a racialised social system when granting the white Afrikaners self-government back in 1910.
And in the middle of the twentieth century, as the quasi-Nazi South African 'National Party' began to flesh out the Apartheid system, Britain remained one of the country's biggest trading partners and arms suppliers.
The British government, then, was both currently and historically responsible for the oppression of South Africa's non-white majority.
But the British government has never been the same thing as the British people.
A global movement against Apartheid
In November 1959, a number of organisations, among them the 'Movement for Colonial Freedom' - which could boast among its members a young Tony Benn - came together to form a Boycott Committee against South Africa.
This soon morphed into the Anti-Apartheid Movement, which would continue to agitate until the ANC was elected to power in a free South Africa thirty-five years later.
The intervening decades saw the AAM drive a range of colourful, innovative, and increasingly effective campaigns.
In 1970, for example, AAM activists - who endorsed an international boycott of South African sport - disrupted the South African rugby tour of Britain so successfully that Harold Wilson's government stepped in to cancel the South African cricket tour of England scheduled later that year.
It was in the 1980s, however, at a time when Anti-Apartheid activism inside and outside South Africa came increasingly to focus on the person of Nelson Mandela, that the AAM shone brightest.
The Apartheid regime was haemorrhaging international support from even its closest allies, and looked increasingly ready to collapse.
Meanwhile, the still-imprisoned figure of Mandela offered not only a symbol of Apartheid's repressive nature but also a strong potential leader of a postcolonial South Africa.
Freeing Mandela and freeing South Africa
In Britain, the AAM established a 'Free Nelson Mandela Co-ordinating Committee' in 1983 for all the many organisations agitating for his release. Thousands of people were encouraged to send him postcards, and concerts and marches were organised.
The movement brought in tens of thousands from across British society.
Left-wing politicians - not least the current Labour Party leader - were a big presence. So were trade unionists and clergy. Students, too, played a role – the Wadham College Student Union at Oxford, for example, started to play the new 'Free Nelson Mandela' song by The Specials at the end of its discos as a gesture of support.
All this pressure from Britain combined with similar activism from across the world until, on 11th February 1991, the Apartheid rulers gave in and released Nelson Mandela after almost three decades in jail.
Three years later he was elected President of the Republic of South Africa in a landslide victory.
On Mandela's 100th birthday, then, we would do well to reflect on how incredibly effective internationalist activism can be.