Immigration
On the eve of World War I, close to 60% of the industrial labor force was foreign-born. In the 19th century, much of the overseas migration had come from the industrial districts of northern and western Europe. Immigrants had been driven from their European farms and towns several forces, including the undermining of subsistence farming by commercial agriculture; a falling death rate that brought a shortage of land; religious and political prosecution. American corporations also sent agents to recruit cheap labor. Not all new immigrants came from Europe there are others who come from Canada, Mexico, and Japan.
http://msbaloghsarchives.edublogs.org/lesson-two-feb-89-rising-tide-of-immigration/