1642: Georgeana (York) in Maine becomes the 1st incorporated American city
1780: Pennsylvania becomes 1st US state to abolish slavery (for newborns only)
1847: Michigan becomes 1st English-speaking jurisdiction to abolish the death penalty (except for treason against the state)
1869: US Postage stamps showing scenes issued for 1st time. These pictorials showed a post horse and rider, a locomotive, a shield, an eagle and a ship, the Adriatic.
1872: Yellowstone becomes the world’s 1st national park
1954: US explodes Castle Bravo, a 15 megaton hydrogen bomb at Bikini Atoll, which accidentally became the most powerful nuclear device ever detonated by the US