The Great Plains is a big area in the middle of the United States that has a lot of grass and not many trees. Long time ago, lots of people lived there, but now there aren't as many. This happened because there were big changes in the way people lived and worked.
A long time ago, people used horses and other animals to farm the land and grow crops. The Great Plains was a good place for this because there was a lot of land to use. But as time went on, new inventions were made that helped people farm faster and with less work. Machines like tractors and combines made it easier to farm, but they also meant that fewer people were needed to do the work.
Another reason why people left the Great Plains was because the weather could be really tough. Sometimes there were long periods of drought, which is when there isn't enough rain. This meant that the crops wouldn't grow and people didn't have enough food to eat.
The government also played a role in depopulating the Great Plains. In the 1930s, there was a program called the Dust Bowl, which was meant to help farmers in the Great Plains. But instead, it made things worse. The government paid farmers to plow up the grasses that held the soil together, and this made it easier for the wind to blow away the topsoil. This caused big dust storms that covered everything in dust and made it hard to live in the area.
All of these things together made it hard for people to live in the Great Plains, so some of them left to find work and a better life in other parts of the country. This is why there aren't as many people living in the Great Plains today.