The development of cheap, versatile steel in the second half of the nineteenth century changed those rules. America was in the midst of rapid social and economic growth that made for great opportunities in architectural design. A much more urbanized society was forming and the society called out for new, larger buildings. The mass production of steel was the main driving force behind the ability to build skyscrapers during the mid-1880s. By assembling a framework of steel girders, architects and builders could create tall, slender buildings with a strong and relatively lightweight steel skeleton. The rest of the building elements—walls, floors, ceilings, and windows—were suspended from the skeleton, which carried the weight. This new way of constructing buildings, so-called "column-frame" construction, pushed them up rather than out. The steel weight-bearing frame allowed not just taller buildings, but permitted much larger windows, which meant more daylight reaching interior spaces. Interior walls became thinner, which created more usable (and rentable) floor space.