When Joe Frazier and Muhammad Ali faced each other in the ring on March 8, 1971, the world stopped to watch. Dubbed “the Fight of the Century,” the clash sold out Madison Square Garden in New York City, grossed $45 million in tickets at closed-circuit venues in the United States alone, and was viewed by over 300 million people worldwide. Even when the result was already known, half the population of the United Kingdom watched a replay on the BBC.

And with good reason. It was a battle for the heavyweight championship of the world—a crown that has been dubbed the greatest prize in sport—between two undefeated fighters and former Olympic gold medalists. But the Fight of the Century was more than just a sanctioned combat between two men: it became a proxy battle for a divided nation.

Born Cassius Marcellus Clay in Louisville, Kentucky in 1942, Ali won gold at the Rome Olympics in 1960 and in February 1964 became world heavyweight champion by defeating Sonny Liston. The day after the Liston victory, Ali rejected the name Cassius Clay given to his family by a slave owner and revealed he had joined the Nation of Islam.

Ali’s reign unfolded against the backdrop of a nation tearing itself apart over civil rights and the war in Vietnam, and the champ soon found himself at the nexus of them all when, having initially been rejected for military service, he was ordered to report before the draft board. Confronted by reporters when the news broke, Ali questioned why he should fly thousands of miles to kill people on behalf of a country that treated him and his fellow African Americans as second class citizens.

“If I thought that my going to Vietnam would help any of the millions of Black people in this country,” he declared, “you wouldn’t have to send for me, I’d go. But it won’t. Going to war with these people won’t help my people one bit. I’d rather go to jail.” For good measure, he proclaimed that, “I ain’t got no quarrel with them Viet Cong.”

On April 28, 1967, Ali made his refusal to join the armed forces formal, claiming conscientious objector status. That same day, the New York State Athletic Commission withdrew his boxing license and stripped him of his title. Boxing commissions across the country refused to allow him to fight in their jurisdictions, effectively banishing Ali from the sport.

Not until late 1970, after the tide of public opinion had turned strongly against the war, did he fight again, granted a license by a specially formed commission in the city of Atlanta over the vociferous objections of Georgia Governor Lester Maddox, who declared fight night a “day of mourning.” Two courts had upheld the government’s refusal to accept Ali’s conscientious objector status, and now the case was making its way to the Supreme Court, where it was slated to be held in June 1971. Fully expecting the decision to go against him, Ali knew he had little time to lose, and so after one more fight, he trained his sights on the man who had ascended to his throne while he had been in exile.

The son of sharecroppers, Joe Frazier left home at age 15 to learn to box, becoming Olympic champion in 1964. He was in many ways Ali’s antithesis: whereas Ali was a loquacious showman, Frazier, in the words of broadcaster Tim Ryan—who called his fight with Ali for Armed Forces Radio—“was a workaday guy, who lived the way he fought: just get in there, throw a hundred punches, be strong, and mind your own business.”

He had not made any political statements or tied his colors to any mast; he had even helped Ali financially during his rival’s banishment and appealed to President Richard Nixon to grant him clemency. But, purely by dint of his not being Ali, he became the unwitting hero of the establishment. Wrote Jerry Izenberg in Once There Were Giants: The Golden Age of Heavyweight Boxing, “many whites who disliked Ali on racial grounds adopted Frazier as their designated Black representative.”

Ali piled on, deriding Frazier as too stupid and too ugly to be heavyweight champion and even, in the ultimate insult, dismissing him as an “Uncle Tom.” Tensions were high: Izenberg, who had written several columns for the Newark Star-Ledger supporting Ali’s stance on the war, had his car windshield smashed in. It was, he noted, hippies against hard hats, the young generation against their elders, all of them using Ali and Frazier as cyphers and forgetting that, “as dramatic as the story was, this was still just a prize fight between two very good heavyweight boxers.”

When fight night arrived, it was as much of an event as anticipated.

“Everybody who was anybody was there,” remembered boxing historian Bert Sugar. “They were scalping hundred-dollar tickets for a thousand dollars outside … There were people coming in with white ermine coats and matching hats, and that was just the guys. Limousines lined up at Madison Square Garden for what seemed like 50 blocks.”

“It wasn’t a normal fight crowd, even for a heavyweight title fight,” recalls Ryan, author of On Someone Else’s Nickel: A Life in Television, Sports, and Travel. “Here, you had people like the Cardinal of New York. There, you had the superstars like Diana Ross. Frank Sinatra was a ringside photographer for Life Magazine. Burt Lancaster was the color commentator on the TV pay-per-view.”

The fight itself lived up to the hype. Ali took control early, but by the sixth he began to tire, weakened by the long layoff and by Frazier’s punches. But even in the ring he continued the verbal taunting he had deployed during the build-up.

“Fool, don’t you know that God’s ordained I be champion?” he said during the 15th and final round.

“Well, God’s gonna get his ass whupped tonight,” retorted Frazier, who dipped and launched a left hook that exploded on Ali’s jaw, sending him to the canvas. Ali hauled himself up, but the knockdown ensured he would lose the round and the fight.

For those who had not only rooted for him but seen a part of them in him, who had raised him up as a symbol of resistance, it was a devastating blow.

“It was awful,” sports journalist and broadcaster Bryant Gumbel said in Thomas Hauser’s book Muhammad Ali: His Life and Times. “I felt as though everything I stood for had been beaten down and trampled.”

In the end, for all the import and symbolism that had been assigned to it, the Fight of the Century was, as Izenberg had written, just a fight. The Vietnam War continued for another four years; 50 years later, America remains riven by racial injustice, and sport figures continue to use their platforms to call for social and political change

Ali had lost the fight with Frazier. But three months later, he won his battle against the U.S. government when the Supreme Court ruled that it had not provided good reason to deny Ali conscientious objector status. He was free to continue his boxing career, which he did to great effect, reclaiming the heavyweight crown from George Foreman—who had taken it from Frazier—in the famous “Rumble in the Jungle” in Zaire in 1974.

The year after, he and Frazier met again, in sweltering conditions in Manila; the two men rained blows on each other for 14 brutal rounds until Frazier’s corner intervened to save their man, his eyes almost completely closed, from further punishment.

Both continued to box, but neither was remotely the same again. Ali and Frazier in many ways made each other; ultimately, they destroyed each other. Frazier never forgave Ali for his taunts and insults; asked what he thought of Ali lighting the cauldron at the 1996 Olympic Games, he hissed, “They should have pushed him in.”

In the eyes of others, their battles may have been representative of a broader conflict; for Muhammad Ali and Joe Frazier, they were intensely personal.

“They did not fight for the heavyweight title of the world,” noted Izenberg after the Manila fight. “The way they fought, they were fighting for the championship of each other. They could have fought on a melting ice floe in a phone booth. That wasn’t settled tonight, and even if they fight again, it will never be settled.”