Japan has her own revolution in the early 1850s, transforms overnight into a technological society, and acquires her own Engine (even the Meiji Revolution still took almost 3 decades in Real Life);
The Union and Confederacy split 10 years earlier (without war - something which no politician would have accepted back then);
Neither the Union nor the Confederacy show any territorial expansionism, leaving the Brits to explore the central North American lands before them;
Karl Marx raises himself to fame as a philosopher despite having no conditions to breed sponsors and a disenfranchised working class as he witnessed in Real Life;
France becomes an Empire at the same moment as in Real Life and they still aim to conquer Mexico, just 10 years too quickly;
Inferred Holocaust: the steampunk dream of a Victorian information age is somewhat deconstructed by the heavy hints that they're using it to catalogue people for the purposes of the then-popular doctrine of eugenics. The ending (set in the 1990's) implies that what's left of humanity only exists as simulated information.