You had to be there, I guess, to appreciate the significance of the first Muhammad Ali-Joe Frazier fight, on March 8, 1971. Not necessarily at ringside, but aware of the mood of the country. It was as if a civil war was being vicariously fought in Madison Square Garden, with each side represented by its champion.

In Ali’s corner were opponents of the Vietnam War, blacks fed up with second-class-citizen status, a large contingent of intellectuals and artists and college kids, affluent liberal types, and people who simply thought Ali was the coolest man on the planet.

Frazier appealed to the World War II generation of working-class whites and blacks who didn’t like Ali’s flamboyant outspokenness. Frazier was the real Rocky, a guy who became a great fighter through sheer force of will. He was also a strong black man who didn’t seem threatening to whites who already felt threatened by “uppity” blacks.

The backdrop, in a nutshell: I was a kid growing up in white working-class Philly and can’t remember a single adult in that little world ever calling Ali by any other name than Cassius Clay, even though he’d changed his name years earlier and everyone knew it.

The bout lived up to its billing as “the fight of the century.” The whole world watched two of the best heavyweights in boxing history slug it out for 15 rounds. Frazier won the decision because he flattened Ali with a vicious left hook in the last round.

Ali and Frazier half-killed each other — there were two more fights, both won by Ali — and their war of words, begun before the first fight and fueled partly by the social strife that defined the era in which they fought, persisted after they retired. Ali outlived Frazier but has suffered from Parkinson’s disease for a long time.

Stan Hochman, a long-time sportswriter for Philadelphia Daily News, neatly summed up their epic story the day after Frazier died:

They brought out the best in each other in the ring and the worst in each other outside the ring. And now Frazier is gone and Ali cannot put two sentences together to mourn our loss. And that is terribly sad.

It’s also sad that the societal divisions that helped make the Ali-Frazier rivalry so bitter and symbolically weighty have grown drastically worse in the 40 years since their first fight. The discontent of the poor and near-poor, dormant for decades, has been rekindled by the widespread realization that the rich have slyly encouraged these divisions — between poor and middle-class, black and white — in order to distract us from the fact that they’re robbing us all. (I’ve just described the genesis of the Occupy Wall Street movement.)

I don’t know if Frazier would see it that way, but one thing’s for sure — he didn’t tolerate anyone making a fool of him, in or out of the ring, and he never backed down from a fight.