What were the first human-made shelters called and what were they made of? ancient people

The first human-made shelters called pit houses. They were pits in the ground with roofs of branches and leaves. permanent structures of wood, stone, or clay or other materials. Even bones from large animals such as mammoths were used in buildingshelters.

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.