The risks and uncertainties of free labor didn't deter millions of immigrants from entering the US during the 1840s and 1850s. Almost 4.5 million immigrants arrived between 1840 and 1860, 6 times more than had come during the previous 2 decades. By 1860, foreign born residents made up about 1/8 of the US population, a fraction that held steady well into the 20th century. Nearly ¾ of the immigrants who arrived in the US during this time came from Germany or Ireland.
