Distúrbios de 24 em 24 anos?

The Long Hot Summer of 2015, por Philip Jenkins (The American Conservative):

Over the past century or so, racially-based rioting in the U.S. has followed chronological patterns that are remarkably consistent, although the reasons underlying these cycles are anything but clear. Particularly serious and major events occur at intervals of about 48 years, with more minor and sporadic outbreaks at the mid-point of that long cycle. Do understand that I am not offering any mystical forms of numerological interpretation here. I merely remark that, for whatever reasons, events have followed this pattern.
Although the pattern can be traced back into the mid-1890s, we might begin our observation in 1919, the hideous year of racial rioting and lethal pogroms in Chicago, Omaha, Knoxville, and other centers. James Weldon Johnson memorably called it the Red Summer. Moving forward 24 years, we note serious but more localized outbreaks of racial conflict in 1943, with upheavals in Harlem and Detroit.

Another 24 years beyond that takes us to 1967, by far the worst year of the urban rioting of that decade. That was the legendary Long Hot Summer, when observers tabulated 159 riots across the nation. It was in 1967 that Newark burned, while the U.S. government sent the 82nd Airborne into Detroit.

Twenty-four years later, historically-inclined observers breathed a sigh of relief when 1991 passed without any grave outbreaks. The following Spring, though, brought the Los Angeles riots, and many lesser copycat events around the country. I stress that the pattern suggests gaps of roughly 24 years, rather than following a precise chronology.

It is not difficult to trace long-term historical patterns and even mystical dates. All you need to is to cherry-pick particular events, while ignoring others that do not fit the scheme. In this case, though, a pattern seems to emerge without such special pleading, as is suggested by the rarity of riots between the various peak years. (...)

Assuming they are grounded in some reality, what might account for such cycles? The obvious linkage is demographic, in that 24 years is roughly the span of a generation. We might for instance suggest that racial tensions rise to the point where they provoke severe violence, but that violence has far-reaching consequences. The sheer scale of loss and destruction deters people from seeking any recurrence of the event. Meanwhile, governments act to prevent such repetitions. The 1943 riots profoundly affected the thinking of liberals, inspiring the civil rights drive of the following two decades. Over time, though, new generations arise, lacking direct memories of the earlier carnage, and thus prepared to risk open confrontations with authority.