Skyscrapers were invented in the US in the 1870s in major cities like Chicago and New York. They were made of structural iron and steel instead of masonry. Builders faced challenges with safety, wind resistance, ventilation, and transportation within tall buildings. By the late 19th century, skyscrapers were understood to be steel-framed structures. Between 1902-1931, New York competed to build the tallest building, though height became controversial. Downsides of skyscrapers included overcrowding, lack of sunlight, and impersonal cities. Urbanization and immigration overwhelmed housing, leading to widespread slums with unsanitary multi-family dwellings and disease.