It’s often good fun and sometimes revealing to divide American history into distinct periods of uniform length. In working on my forthcoming book on American migrations, internal and immigrant, it occurred to me that you could do this using the American-sounding interval of 76 years, just a few years more than the Biblical lifespan of three score and 10.

It was 76 years from Washington’s first inaugural in 1789 to Lincoln’s second inaugural in 1865. It was 76 years from the surrender at Appomattox Courthouse in 1865 to the attack at Pearl Harbor in 1941.

Going backward, it was 76 years from the first inaugural in 1789 to the Treaty of Utrecht in 1713, which settled one of the British-French colonial wars. And going 76 years back from Utrecht takes you to 1637, when the Virginia and Massachusetts Bay colonies were just getting organized.