Complex sentence: What were termed "owl wagons" in 1880s, became furnished, fixed ex-streetcar late "nightowl" diners, which proliferated in New York City when drinking alcohol was prohibited by the Volstead Act from 1920-1933.
Split into simpler sentences: What were termed "owl wagons" in the 1880s became furnished, fixed, owl dining cars. These proliferated in New York City when drinking alcohol was prohibited by the Volstead Act from 1920-1933.