During the last quarter of the 19th century, large numbers of immigrants were admitted to the united states primarily because of the economy's need for more:

We were in the need of more Labor. The Industrial Revolution had brought us many ways to more quickly create goods. However, we still needed the man power to run the various machines involved. We also still had resources that had to be gotten by hand; farm labor, mining, logging. The many natural resources meant more men were needed so that they could get at the material to use for various things and sell to other nations.