Although divided by stylistic eclecticism, the United States took the lead in the development of advanced building technologies in the second half of the 19th cent. Engineering became a distinctly separate profession, and works such as the Brooklyn Bridge by John and Washington Roebling (1869–83) number among the most impressive of all American achievements. The technical innovations of this era included the use of cast iron, steel, and reinforced concrete in construction.
The trend toward functional design, which had been steadily growing, reached its greatest expression in the works of the so-called Chicago school of architecture led by Louis Henry Sullivan. Sullivan broke completely with historical eclecticism and used modern materials in such a way as to emphasize their function. The commercial buildings and skyscrapers of Chicago and other cities built under his influence were admired for their power and originality as well as for the rational organization of their parts.