The spread and development of industry in the United States, as well as areas of favorable climate were factors responsible to change population patterns in America.
Specially during the late years of the 19th century and the World Wars, the need for workers grew significantly with a growth in production and industrial development, and that's attracted many people (that moved from countryside regions and settlements to major cities). Favorable climate conditions has attracted farmers and businesses for generations; with a constant growth in demand for supplies, raw materials and food, areas with good climate conditions are seen as opportunities for profit.
That's why these 2 factors (industry and climate) are responsible for the changes that occurred in the population patterns in the US.
As most of the initial fighting took place in Europe and the Soviet Union and United States took several years to get involved France and Britain were the main Allied Powers at the beginning of World War II.
