This could have tremendous effect on people. It's BretVictoresque stuff, things that could expand the space of thoughts we have, and vastly increase our comprehention of information available.
>To my former memory, the United States had always existed—there was never a time when there was no United States. I had not remembered, until that time, how the Roman Empire rose, and brought peace and order, and lasted through so many centuries, until I forgot that things had ever been otherwise; and yet the Empire fell, and barbarians overran my city, and the learning that I had possessed was lost. The modern world became more fragile to my eyes; it was not the first modern world.
>So many mistakes, made over and over and over again, because I did not remember making them, in every era I never lived...
"CENTENNIA is a map-based guide to the history of Europe and the Middle East from the beginning of the 11th century to the present. It is a dynamic, animated historical atlas including over 9,000 border changes. The map controls evolve the map forward or backward in time bringing the static map to life. Our maps display every major war and territorial conflict displaying the status of each region at intervals of a tenth of a year."
(note all the "somehows")
In the end I took on a similar but much less difficult problem but the original idea has always been at the back of my mind.
Too bad I am not competent enough to actually build something like this. I would definitely be up for helping out, though.