Why are the majority of the world's economies mixed? What may happen to the "pure" types of economies (traditional, socialist/command, market capitalist) when they incorporate elements from
other economic models?

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.