Boycotts also had a deep effect on the Olympics, both in 1980 - when the United States, China and numerous other countries refused to compete at the Moscow Games following Russia's 1979 invasion of Afghanistan - and in 1984, when Russia and 14 other sympathetic nations in turn snubbed the Los Angeles Games.

But the Games that took place 50 years ago in Mexico City were perhaps the most politically fraught, given the huge forces of historical events bearing down upon them.

Interviewed in the 1999 HBO Sports documentary Fists of Freedom: The Story of the ’68 Summer Games, United States athlete Larry James, who won 400 metres silver and 4x400m gold at those Olympics, said: "It was cram-packed with enough events to cover the whole century."

Large parts of the world were in political turmoil in the months leading up to that quadrennial sporting event, which took place from October 12 to 27. In the US, widespread protests against the Vietnam War, involving students and others within the Peace Movement, were rising.

In April, Martin Luther King, the charismatic head of the American civil rights movement, who had used non-violent means for years to campaign against racial inequality, was shot dead. That led to riots in 125 US cities including Baltimore, Washington D.C and New York City. National politics was brutally jolted in June by the assassination of Bobby Kennedy as he ran for the Presidency.

In Europe there were mass student protests, most notably in France, where people battled with police on the streets and were soon joined by workers demonstrating against the De Gaulle Government. The protests prompted a general strike that involved more than 10 million people.

Elsewhere in Europe, Czechoslovakia's attempt to free itself from a Communist regime was crushed by an invasion of Soviet troops.

And in Mexico itself there were ominous signs within a large student population that was also calling for greater democracy in the face of an authoritarian regime, while protesting against economic measures that had been taken against labour unions. As the Government prepared for a Games that it hoped would enhance its standing in the world and its growing trade links following the economic growth that was known as the Mexican Miracle, the students were pulling in the opposite direction.

In August a series of protest marches took place in Mexico City involving around half a million people. President Gustavo Diaz Ordaz, who would open the Games less than two months later, ordered the occupation of the National Autonomous University of Mexico. But the protests continued.

The student organisers were well aware of the fact that world attention was falling on Mexico in the run-up to the Olympics. On October 2, 10 days before the Games were due to start, thousands of students massed in the Plaza de last Tres Culturas in the Tlatelolco area of Mexico City to call for greater civil and democratic rights. Their views on the coming Olympics were clear from their banners: ¡No queremos olimpiadas, queremos revolución!  - "we don't want Olympics, we want revolution".

Around 5,000 soldiers surrounded the Plaza and, in circumstances that have still not been definitively clarified, shooting began. Eyewitnesses, including some members of the European media including The Guardian’s then athletics correspondent John Rodda, who was caught on a balcony as the shots rang out and had to duck in a hurry, maintain hundreds of protesters and civilians were killed and many arrested.

Among those present was Italian journalist Oriana Fallaci, a special correspondent for the political magazine L’Europeo, who was shot three times by Mexican soldiers, dragged downstairs by her hair and left for dead. Her eyewitness account became important evidence in the face of the Government's denials that a massacre had taken place.

There has been subsequent speculation that the firing started when Government snipers positioned around the plaza took aim at the surrounding soldiers. Others have claimed that events tipped over when flares were dropped on the crowd from a helicopter.

The initial official figure was that four had died. That figure was later revised to just over 300.

The shock waves from this savage occurrence continued to ripple through Mexican society, and world opinion, as the Games started - and started without South Africa.

Banned from the 1964 Tokyo Olympics by the International Olympic Committee (IOC) because of its apartheid system, South Africa had been provisionally invited to the 1968 Games on the understanding that all segregation and discrimination in its sport would be eliminated by the time of the 1972 Olympics.

However, African countries and African-American athletes promised to boycott the Mexico Games if South Africa was present, as did eastern-bloc countries. In April 1968, the IOC conceded that "it would be most unwise for South Africa to participate".

South Africa would remain isolated from the Games, and much of world sport, until the ending of the apartheid system allowed its return to compete in the 1992 Barcelona Olympics.

Once the sport got underway at the Games, it was not long before politics reared its ugly head again. Or in this case, its beautiful head.

The gymnastics career of Věra Čáslavská, the seven-times Olympic champion who died in August 2016 aged 74, will live on in history. But above and beyond her sporting achievement is the memory of how she effectively ended that career at the 1968 Mexico City Games with a podium protest against the Soviet Union, whose forces had invaded her homeland of Czechoslovakia two months earlier.

Having won the all-around, vault and beam golds at Tokyo 1964, Čáslavská completed her set in Mexico as she retained her all-around title by winning the vault again, and the uneven bars, as well as taking joint gold in the floor exercise.

The latter event was where her crucial action occurred. Originally adjudged as winner, she was going up to receive her medal when it was announced that the score of the Soviet Union's Larisa Petrik had been upgraded and the title was to be shared.

When the Soviet Union's national anthem was played, Čáslavská stood with her head down and turned away in a silent but unmistakable protest.

Earlier in the Games after another very controversial judging decision that had cost her gold on beam - with Soviet rival Natalia Kuchinskaya taking the title - Čáslavská had also turned her head down and away during the playing of the Soviet national anthem.

Upon her return to a country under Soviet rule she gave her four golds to the Czech leaders of the Prague Spring - the doomed attempt to liberalise the Communist regime that had been established by a coup d'etat in 1948.

The podium demonstrations had already settled her fate, and after that defiant homecoming there was no chance of any other outcome. Čáslavská was shunned by the establishment for more than 20 years, losing her job and her right to travel until the changes brought about by the fall of the Berlin Wall re-established her in triumphant fashion.

In making that point on the podium, Čáslavská had defied not only the Soviet ruling system but the IOC.

Chapter five of the Olympic Charter insists that "no kind of demonstration or political, religious or racial propaganda is permitted in the Olympic areas".

She was not the first, or the last, Olympic athlete to transgress.

The men's 200m final was one of many sprint events in which the thin air of Mexico City - at an altitude of 2,250m, and a first Olympic all-weather track, helped bring about a world record. It was won in 19.83 seconds by Tommie Smith of the US, whose team-mate John Carlos took bronze in 20.10. Silver went to Australia's Peter Norman in a national record of 20.06.

All in all, a memorable Olympic race. The figures, however, are not what it is remembered for. Or at least, not those figures, but instead those of Smith and Carlos standing solemnly on the podium, each holding up a clenched fist in a black glove.

Thus did the most famous individual athlete protests in Olympic history take place as the two US athletes, nobly abetted by the Australian, turned the medal ceremony into a profound political statement of solidarity which effectively ended both of their athletics careers as it drew a furious reaction from, principally, the IOC, but also from many of their fellow Americans.

As they took to the podium, Smith and Carlos were both shoeless but wearing black socks - something they later explained was to represent black poverty. 

Smith wore a black scarf around his neck to represent black pride, Carlos had his tracksuit top undone to show solidarity with all blue collar workers in the US and also wore a necklace of beads which he subsequently described as being "for those individuals that were lynched, or killed, and that no-one said a prayer for, that were hung and tarred".

Each wore a single black glove, which they raised in a fist, with bowed heads, as the Star Spangled Banner anthem played.

All three on the podium, including Norman, who had been a critic of Australia's former White Australia Policy, wore Olympic Project for Human Rights badges. He had suggested that the two US athletes take one glove each after Carlos had accidentally left his pair in the Olympic Village.

 The gesture raised boos from many of the spectators.. Smith later said: "If I win, I am American, not a black American. But if I did something bad, then they would say I am a negro. We are black and we are proud of being black. Black America will understand what we did tonight."

The US National Olympic Committee was leaned upon by the IOC - whose American President, Avery Brundage, later referred to the incident as "the nasty demonstration against the American flag by negroes" - to suspend the athletes and send them home.

US athletes were warned in Mexico that "a repetition of such incidents would warrant the imposition of the severest penalties at the disposal of the US Olympic Committee".

But subsequent protests of varying degrees took place.

After Lee Evans had led home a US clean sweep in the 400m, all three winners wore black berets to their medal ceremony. Bob Beamon, who broke the world record in the long jump, wore black socks pulled up high at his ceremony, while fellow US bronze medallist Ralph Boston went barefoot and said: "they're going to have to send me home too". He was not sent home.

As a postscript, the US women's 4x100m relay team publicly dedicated their own gold medals to Carlos and Smith.

Wyomia Tyus, the US sprinter who followed up her Tokyo 1964 triumph with victory in Mexico four years later, told NBC Sports how, at a US team meeting, other black athletes felt the message was "you can do whatever you want - what they have done, that said everything right there". 

Tyus herself wore black running shorts in that relay final, where she ran the anchor leg as the US won in a world record of 42.88, although she adds that she was not sure anyone had noticed.

But when the team were asked afterwards by the press what they thought about the Smith and Carlos protest, Tyus replied: "What is there to think? They made a statement.

"We all know that we're fighting for human rights. That's what they stood for on the victory stand - human rights for everyone, everywhere. And to support that and to support them, I'm dedicating my medal to them. I believe in what they did."

In the 1999 HBO documentary, Smith reflected: "We were not Antichrists. 

"We were just human beings who saw a need to bring attention to the inequality in our country.

"I don't like the idea of people looking at it as negative. There was nothing but a raised fist in the air and a bowed head, acknowledging the American flag - not symbolising a hatred for it."

Smith and Carlos received death threats in the wake of their protest, and the latter's home was attacked.

Norman recalled how, in the immediate aftermath of the protest, he was protected by his team manager, Julius Patching. "With a smile, [he] told me to consider myself severely reprimanded," he said. "Then he asked me how many tickets I wanted for the hockey."

Patching, however, had work to do to protect his athlete from conservative politicians back home in Australia who were calling for his blood. Despite running the Olympic qualifying time in 1972 and finishing third in the trials, while suffering from a knee injury, Norman did not go to Munich. No male sprinters were selected by Australia. He retired soon afterwards.

Norman was not included in the official celebrations when Sydney staged the 2000 Olympics. He died of a heart attack in 2006.

The Australian Olympic Committee (AOC) did not apply any official sanction to Norman for his Mexico actions, and the body has since denied that he was not picked for Munich because of what had happened four years earlier.

Regarding Sydney, the AOC commented in 2015 that it "was not in a financial position to invite all Olympians to Sydney 2000". They were given special assistance to purchase tickets but it would have cost the AOC hundreds of thousands of dollars to bring Olympians from around the country to Sydney for the Games, it was claimed.

"The suggestion he was shunned is totally incorrect," the AOC said. "He was treated like any other Australian Olympian."

Whether that was true in Norman’s life is debatable. "If we were getting beat up, Peter was facing an entire country and suffering alone," Carlos once said.

It certainly was not true after Norman died. In 2012 the Australian Parliament debated a motion to provide him with a posthumous apology "for the treatment he received upon his return to Australia, and the failure to fully recognise his inspirational role before his untimely death in 2006".

In June this year the AOC presented Norman's family with an Order of Merit - its highest award - to acknowledge his support for the civil rights protest.

And earlier this week it was announced that a bronze statue of Norman will be erected at the Lakeside Stadium in Melbourne.

When Norman died, Smith and Carlos acted as pallbearers and Carlos recounted the conversation the three of them had before going out for the medal ceremony.

He said he and Smith had asked Norman if he believed in human rights, and he had said he did. He said they asked him if he believed in God and Norman, who came from a Salvation Army background, had said he believed strongly in God.

"We knew that what we were going to do was far greater than any athletic feat," Carlos recalled.  "Peter said, 'I'll stand with you.'"

Carlos added that he had expected to see fear in Norman's eyes, but did not. 

"I saw love," he said.