What is meant by "drawing the color line"?

After the congress of vienna europe

Which of the following led to a continuation of the treatment in the excerpt above? a)the brutality of the trans-atlantic african slave trade. b)spanish repression after violent native uprisings in new spain during the 16th century. c)european competition to quickly establish colonial holdings in the new world. d)the reliance of the spanish on native americans to provide labor under the encomienda system.

The communists triumphed over forces because of a well-disciplined fighting force, a single - minded sense of zeal , and strong convictions.