U.S. boxing heavyweight champion Muhammad Ali is pictured on Oct. 19, 1974, 11 days before the heavyweight world championship in Kinshasa, Congo. (AFP via Getty Images)

Over the weekend, tributes came flooding in from the United States and, indeed, the rest of the world after the passing of the great boxer Muhammad Ali. The sporting icon was as loved for his bravado outside the ring as his prowess inside it. And the importance of his revolutionary politics ought not to be understated.

Much has already been written about both Ali's faith — he converted to Islam in 1964 — as well as his championing of black power at a time when America's racial wounds were rawer than they are now. His outspokenness made him an emblem for those struggling in the margins of Western society or emerging from under the yoke of Western empire overseas.

It's for that, noted President Obama in a statement posted on Facebook, that Muhammad Ali is "a name as familiar to the downtrodden in the slums of Southeast Asia and the villages of Africa as it was to cheering crowds in Madison Square Garden."

Numerous world leaders, including Turkish President Recep Tayyip Erdogan and King Abdullah II of Jordan, intend to attend Ali's public memorial on Friday in Kentucky.

The leader of Kenya’s political opposition, Raila Odinga, said in a statement over the weekend: “Muhammad Ali fought for the emancipation of the black race not only in the U.S. but also in many African nations then under the yoke of colonialism.”

“Together with Nelson Mandela, Ali was a source of inspiration for those who pursue justice, those seeking equal opportunities, the downtrodden and those seeking fairness in sport and society,” Danny Jordaan, the head of South Africa’s soccer federation, said in a statement.

Ali's politics crystallized around his resistance to the draft and his opposition to the Vietnam War.

"When he refused induction in the United States Army, he stood up for the proposition that unless you have a very good reason for killing people, war is wrong," his biographer Thomas Hauser said in an interview with CBS.

Ali "forced Americans to think about the moral consequences of killing other human beings half a world away who really had nothing to do with us," writes Rolling Stone columnist Matt Taibi. "But a generation later, we Americans mostly lack the instinct to even ponder those questions. We sit through movies like 'American Sniper' that tell us that Iraqis are villains because they shoot at our soldiers. The question of why we were ever there in the first place to shoot or be shot at is not talked about as much."

But it was also more than that: Ali, like the leftist ideologues of his era, saw a connection between American militarism and Western imperialism abroad and systemic racial injustice and oppression at home.

"Man, I ain't got no quarrel with them Viet Cong," he famously exclaimed. "No Viet Cong ever called me nigger."

At a 1967 event in Howard University, noted The Washington Post at the time, African American students coming to hear Ali speak wore "togas and shawls" and brandished copies of Frantz Fanon's "The Wretched of the Earth," a fiery tract on anti-colonial struggle rooted in Algeria's successful war for independence from France.

That same year, he delivered a statement in his home town of Louisville on why he wouldn't go to Vietnam. It's worth reading at length:

“Why should they ask me to put on a uniform and go 10,000 miles from home and drop bombs and bullets on brown people in Vietnam while so-called Negro people in Louisville are treated like dogs and denied simple human rights? No, I’m not going 10,000 miles from home to help murder and burn another poor nation simply to continue the domination of white slave masters of the darker people the world over. This is the day when such evils must come to an end. I have been warned that to take such a stand would cost me millions of dollars. But I have said it once and I will say it again: The real enemy of my people is here. ... If I thought the war was going to bring freedom and equality to 22 million of my people, they wouldn’t have to draft me, I’d join tomorrow. ... I have nothing to lose by standing up for my beliefs. So I’ll go to jail, so what? We’ve been in jail for 400 years.”

This led to his arrest and ostracism from the boxing community, as well as denunciation by both the political and sporting establishments.

Legendary sportswriter Red Smith likened Ali to "those unwashed punks who picket and demonstrate."

TV host David Susskind branded him "a simplistic fool and a pawn" during a broadcast in which the boxer was beamed in via satellite, cited by the Atlantic.

"I find nothing amusing or interesting or tolerable about this man," Susskind said. "He’s a disgrace to his country, his race, and what he laughingly describes as his profession."

Susskind's smug view seems utterly laughable now, a curious souvenir from the wrong side of history. But the angry rejection of Ali's politics reflects attitudes that linger across generations.

You can hear strains of this in the rhetoric of Republican presumptive presidential nominee Donald Trump, whose appeals to the good old days carry a racial coding and whose trumpeting of Western values and military might play to a nostalgia for lost hegemony. And you hear it across the pond, where influential British politician Boris Johnson can pin a disagreement with Obama over Britain's place in the European Union on "the part-Kenyan president’s ancestral dislike of the British empire."

Ali would have no time for that. "I am America," he declared. "I am the part you won't recognize. But get used to me."

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