Tōkyō grew tremendously during the 20th century (except for a temporary but severe dip during World War II). The urban area expanded first to encompass (and eventually merge with) its prefecture, and then to reach beyond it, especially to the north, east and south.
The urban area that included the cities of Ōsaka, Kyōto and Kōbe grew and merged during the second half of the 20th century to form the Keihanshin metropolitan area. Ōsaka grew as a heavy industrial center during the first four decades of the 20th century. Nagoya also grew as an industrial center before World War II and its metropolitan area continued to grow after. The urban areas of Fukuoka Prefecture also grew and merged during the second half of the 20th century, forming the Fukuoka-Kitakyushu metropolitan area.