An alternate history may or may not be pinned down to a year of real chronology or to a specific real town or country.
Nonetheless, most steampunk writers inform their choices of manners, politics, geography, science, etc with a study of one or more eras.
If one were to survey the globe from the mid-1800's to the early 1900's, some highlights would include:
Victorian Era, 1837 - 1901
Gold Rush of the 1840's, Gilded Age, and start of Progressive Era
France (and 'the Continent')
La Belle Epoque - end of the Franco-Prussian War to the start of WW I
late Edo period (to 1868) and Meiji (1868- 1912)
late Qing dynasty (1644 to 1911)
largely occupied by the East India Company's private army, supplanted by British military in 1857
waning decades of the Ottoman Empire