Some early skyscrapers have a steel frame that enables the construction of load-bearing walls taller than of those made of reinforced concrete. Modern skyscrapers' walls are not load-bearing, and most skyscrapers are characterized by large surface areas of windows made possible by steel frames and curtain walls.The development of skyscrapers came as a result of the coincidence of several technological and social developments.
It was the refinement of the Bessemer process, first used in the United States in the 1860s, that allowed for the major advance in skyscraper construction. As steel is stronger and lighter in weight than iron, the use of a steel frame made possible the construction of truly tall buildings.
The Long March was indeed a revolutionary withdrawal to avoid the prosecution of the Kuomintang (KMT or Chinese Progressive Party) army conducted by the Red Army of both the People's Republic of China, the mainstay of the People ’s Liberation.
