The Rise and Fall of American Growth: The U.S. Standard of Living since the Civil War (The Princeton Economic History of the Western World Book 70)

by Robert J. Gordon

Seven-eighths of the 1870 population was white and the remaining eighth black, with virtually no representation of other races. The 1940 population was even more homogenous, with nearly 90 percent white and most of the remainder black, in sharp contrast to the 15 percent in 2010 made up of races other than white or black (primarily Hispanic and Asian, but also people reporting being of two races).

Census numbers probably overstate this homogeneity though because the didn't include mixed race options. White ethnic and religious groups were also far more homogeneous in 2010 than in 1940.