The Democratic Party was one for the people but contained a large southern population.
The Democratic Party in particular those outside of the South wanted to fight for Civil Rights as blacks were part of the "commoner/worker" base the party had focused on since the turn of the 20th century. The Southerners were also still a part of the party due to tradition and farming. However, they were the Jim Crow laws the Civil Rights Movement was fighting. Eventually, the Democrats owned the civil rights laws and the southerners left the party to join the Republicans by 1970.
One important factor that contributed to the Atlantic slave trade during the time of European colonialism was the high demand for labor in places like the Caribbean, where sugar was being harvested due to its high demand in Europe.
