Thanks for the how-manyeth time to the King County Library System (who needs Amazon?), I'm entranced by a book that I wouldn't otherwise have seen: Ferdinand Protzman's "Landscape:photographs of time and place". In commenting on a photo of kites in Ho Chi Minh City by An-My Le, Protzman observes

For many Vietnamese young people the war is a matter of history, not memory.

This takes me back to Santayana's oft-quoted

Those who cannot remember the past are condemned to repeat it.

It's a matter of simple observation that we cannot remember the past; history is practiced as nostalgia or exhortation, not memory. It then follows that Protzman's young Vietnamese, and young people everywhere, are doomed to repeat their war, since they cannot remember it.

This suggests a simple, testable hypothesis for the scale at which history repeats itself.

Once more than half of the population can no longer remember an event but merely learn about it in books, those events are teed up to play themselves out again yet again. Given the events in Iraq, we seem to be nearing the point at which the Vietnam counts as history, not memory. A scarily short cycle time...