Generally speaking, "assembly line jobs" did not represent an obstacle during this time, since this in fact increased productivity through the "specialization of labor".
D). Vast empires.
Classical civilizations developed vast empires, whereas early river valley civilizations did not.
The answer to this question is 28%.
As a nation of immigrants, united States host the most diverse group of people in the world.
Over several years, the immigrants have become a crucial part of our society, but the number is predicted to come down due to development of technology that allow workers to do their job remotely.
The answers that apply to the question would be: John Brown's raid AND the election of 1860. The other events had already happened by the time the civil wat started.