What is contributed most to increased settlement of the great plains?

Answer: A series of federal land grants

Explanation:

Remember the Homestead Act? This was the act that was controversial prior to the Civil War. It had difficulty getting passed because the government was concerned about new states being founded and tipping the balance of free states and slave states. Eventually Lincoln got this law passed. Americans were given acres of land to settle. The land was tough to farm and several new farming machines, such as a mechanical reaper and seeder were established to till the soil. Living out west was tough as people lived in grass huts (remember the letter the farmer sent to his wife trying to boast about how good things were when the really weren't and the advertisement the government put out trying to entice people to settle west)