With abundant natural resources,inventive thinkers, and risk taking entrepreneurs of the United States all contributed to the nations industrial expansion.This expansion would not have been possible, however, without the million of laborers who allowed the companies to succeed.Around 14 million people immigrated to the United states between 1860 and 1900.Most came in the hope of finding work in the country's booming industrial centers.During the civil war,when labor was scarce ,the federal government encouraged immigration by passing the Contract Labor Act in 1864.This law allowed employers would pay to enter into contracts with immigrants.