It was the start of the large powerful American military before WW1 the Entirety of the United States Armed Forces could fit in Yankee Stadium now it is over 1 million members strong
Which war? World war 2? If world war 2, it was due to the fact that their home towns were in rubble, and were looking for a new home for them, and their family.
There are several causes of the Great Depression, in the early 20th century and they have been extensively discussed by economists and remain a matter of active debate.
Actually, there was an initial stock market crash that triggered a "panic sell-off" of assets. This was followed by unemployment, since over 13 million people were unemployed by 1932 and, as a result, there was a terrible impoverishment.
To sum up, the correct answer is letter "D": Tariff and War Debt Policies, Farming Crisis, Income inequality and lack of credit regulation.