Which two countries later joined forces with americans to fight the british?

If you are referring to the war for independence, then the countries should be France and Spain because they were America's main allies versus Britain. Netherlands also supported the US.

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.