Complex sentence: In total, African Americans made over 90 percent of Birmingham's unskilled labor Force by 1910, and by 1920, Black women made up 60 percent of female workers, 87 percent of which were engaged in domestic work.
Split into simpler sentences: In total, African Americans made over 90 percent of Birmingham's unskilled labor Force by 1910. By 1920, Black women made up 60 percent of female workers, and of that 87 percent were engaged in domestic work.