original: By the early 1880s the population was in decline.
simplifications: By the early 1880s the population was reducing. By the 1880s the population was declining. The population declined by the early 1880s. By the early 1880s, the population was falling. By the early 1880s the population was going down. By the early 1880s, less and  less people lived there. By the early 1880s the population was falling. In the 1880s the population declined. The population was in decline by the early 1880s. By the early 1880s, the population had decreased.