is another term for a market economic system.

It's definitely not Capitalism as capitalism is the "opposite" of a market economy - it's a free market economy, not command economy (market economy is the same as command economy).

Actually both Communism and socialism are forms of market economy - perhaps Communism is more typical so it's a better answer but both are correct. 

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.