The United States adopted a policy of isolationism after the First World War. They had lost many men during the conflict and did not want to get involve in another war. They also had to deal with the Depression. They continued this policy until the outbreak of the Second World War.
1930's is the decade which the U.S pursed a policy of isolationism.
windmill
barbed wire
split-rail fencing
Farmers couldn't fence their whole lands at first. It was too pricey and time consuming. Also, farmers, at first, had no reason to fence their lands until the cattle started running over it.
It was when the barbed wire was invented that things changed.
Fencing became much cheaper with barbed wire than with wood and since the cattle could be hurt and even get stuck in the fences, but for sure not go through, it solved the problems of the farmers.