Explain what caused the dust bowl conditions on the great plains

The American Dustbowl in the 1930's, if you are referring to this, was created due to natural drought, strong winds and poor farming practises.

There was an extreme loss in soil fertility due to over-farming the land. Due to the depression, farmers grew lots in order to make a living as prices went down.

The drought and high temperatures that occurred worsened the situation. A lack of water in the soil made it dry, and high temperatures baked the soil even drier.

The actual 'dust' was made by soil erosion. Strong winds blew the top layers of soil into the air due to how poor condition the ground was in. There was nothing holding the top layers of the soil so it just blew away into dust storms.