Detroit's population began to expand rapidly based on resource extraction from around the Great Lakes region, especially lumber and mineral resources. It entered the period of largest and most rapid growth in the early 20th century and through World War II, with the development of the auto industry and related heavy industry. Attracting hundreds of thousands of immigrants from Southern, Central, and Eastern Europe, the Near East, and black and white migrants from the South, the city became a boom town. By 1920 it was the fourth-largest city in the country.