During the early twentieth century, American cities and suburbs underwent significant change. This dissertation examines two architectural projects, Rockefeller Center and Broadacre City, that respectively sought to interpret and intensify competing trends of density and dispersion during the 1930s. Rockefeller Center was designed by an architectural consortium led by Raymond M. Hood. It began in the late 1920s as a project for an opera house adjoined by revenue-producing commercial development. After the October 1929 stock market crash, it became a fourteen-building, office-and-entertainment complex that, when completed in 1939, manifested an argument unequivocally in favor of urban densification. In the spring of 1930, Frank Lloyd Wright began promoting Broadacre City as a framework for managing automobile-induced dispersion. By 1940, he had written several books, given dozens of lectures, and mounted exhibitions (including at Rockefeller Center) that expanded his original ideas into a robust theory of socio-spatial change. Amidst the economic convulsions and social upheavals of the 1930s, these two projects culminated debates about how American cities, the landscapes around them, and the infrastructures that supported them were being reshaped by skyscrapers and suburbanization. This dissertation examines these two works with a twofold aim: to reevaluate the terms on which they have been understood in architectural history and to consider the perceived limits, possibilities, and conditions of change—social, spatial, territorial, technological, cultural, economic—during a tumultuous decade in twentieth century history. This dissertation contends that, despite their familiarity in histories of modern architecture, there are new, critical insights to be gained about Rockefeller Center and Broadacre City and that those insights can be used to elucidate the role architecture has played in mediating social change. Considering these two projects together—in dialogue with one another and in the historical context they shared—shows Rockefeller Center and Broadacre City to be ideal vehicles for understanding the contours and contingencies of architectural and urban discourse and, more broadly, how metropolitan America transformed during the Great Depression.