What was the biggest cause of the dust bowl?

I can't say the biggest cause, but the causes are drought, strong winds, stock market crash, and e. t. c.

If I will say what caused it, It would be the stock market crash or drought.

It depends on the person. If it was a farmer or rural person they will most likely be affected the most by the drought. If it was a business person they will be most likely most affected by the crash of the stock market.