By 1860 the population of the U nited S tates had increased to 31.4 million, and the center of population was m oving steadily westw ard. T he rapid grow th of population was due to a high b irth ra te and to steadily increasing im m igration. By far the m ajority of A m ericans were engaged in agriculture, bu t the beginnings of industrialism and of organized labor could be seen.