Farming.
I am really starting to suspect that in real life you are a public school teacher :)
American History of Oklahoma, briefly
Inhabited by Southern Plains indians
The US government thought it was so shitty the called it Indian Territory and moved all the Eastern tribes there.
Dam immigrants needed land so they put the remaining Indians under the process of termination a term by which the government gave each Indian 160 acres and terminated all rights as a tribe but the government kept the right to buy or sell the Indians land under him and take care of all of his money which promptly dissapeared. They then started the great land rush where settlers staked 160 acre homesteads.
The plains of oklahoma are a piss poor place for farming so a guy would need a thousand acres to make a living. A lot of the homesteaders didnt make it. Drought, insects infestation and poor farming techniques caused a lot of grief.
During the Depression a lot of farms failed for various reasons and the workers migrated to other areas.
As for the poetic license of Steinbeck, What was shown in the movies did happen then just as it happens today. Farm workers are treated worse than cattle
[link|http://www.sptimes.com/News/081601/State/For_slavery__man_to_s.shtml|slavery modern american style]
thanx,
Bill