In a within-groups design, exposing participants to one level of the independent variable can change how they respond to the other levels of the independent variable. This problem is generally referred to as 'carryover,' or.

Accumulating more land so that your country can continue expanding without running into problems such as overpopulation

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.