In addition to the stock market crash of what were the main underlying causes of the great depression? a damage to the nation’s psyche after wwi b people’s consumption habits not keeping up with new technologies c lack of upkeep of infrastructure after wwi due to war debt. d tariff and war debt policies, farming crisis, income inequality, and lack of credit regulation.

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.