However, the advent of makeshift tent communities during the Great Depression caused concern in the Administration. The Federal public housing program was created by the 1937 Act, in which operations were "sustained primarily by tenant rents." As a result, public housing in its earliest decades was usually much more working-class and middle-class and white than it was by the 1970s. Many Americans associate large, multi-story towers with public housing, but early projects were actually low-rise, though Le Corbusier superblocks caught on before World War II.