Complex sentence: In the English-speaking world of the 18th and 19th century, achievement of a parlour room was a marker of social status--evidence that you had risen above the majority who lived in one or two rooms.
Split into simpler sentences: In the English-speaking world of the 18th and 19th century, having a parlour room was evidence of social status. It was proof that one had risen above those who lived in one or two rooms.