The skyscraper (usually defined as a building over 40 stories high) first appeared in Chicago in the 1890s, and was largely an American style in the mid 20th century, but in the 21st century skyscrapers were found in almost every large city on every continent. A new construction technology, the framed tube structure, was first developed in the United States in 1963 by structural engineer Fazlur Rahman Khan of Skimore, Owings and Merrill, which permitted the construction of super-tall buildings, which needed fewer interior walls, had more window space, and could better resist lateral forces, such as strong winds.