A magnificent 1850s house dubbed the Blue Belle of Brooklyn

They could have just repeatedly said "the 1850s" but they wanted to be more diverse. Kind of like how "temblor" gets hauled out every time someone writes about earthquakes.

I'm super-curious if you know of a term for the 1850s that is geographically relevant to New York, or the region?

Also that war had a major impact on NYC, as that city (and Boston) were the major sources of slave mortgages, which were all invalidated at the end of the war.

"Pre-war" is a term of art in real estate, meaning post-WW1/pre-WW2, when the first big apartment buildings went up. Many of these buildings were the work of craft and are desirable residences today.

"Post-war" is also a term of art- post WW2- and generally means ugly/junky, in real estate terms.

Many of the brownstone/single family townhouse/rowhouse neighborhoods were built before and around the WW 1 time frame, 1890s to 1920s.

The need to refer to it is infrequent, but "antebellum"- literally also "pre-war"- is recognizable for pre- but proximate to the Civil War. The Civil War was so momentous, it deserves its own latin reference, lol. In real estate terms few structures remain of course, but it is helpful in terms of history to distinguish from the Revolutionary period (1760s to 1790s) and the immediate post-Revolutionary period, when tons of things happened. 1810 in Manhattan was when the grid plan was laid down and that period through the 1840s saw a huge population boom and the initial transition of NYC real estate from home/workshop of artisans to predominantly income production.