The Democratic Party, since the Civil War, has always been a coalition of victims struggling against an establishment of businessmen and white Protestants. For about a hundred years after the war, the coalition consisted of workers (largely immigrant and Catholic), struggling small farmers, and southern whites. While the last group actually enjoyed a monopoly of power in their region, they felt like victims because they had lost the war and seen their “country” occupied. The defense of slavery and the rights of African-Americans did not, of course, enter into this narrative at all; to southern whites, the war was a noble defense of a traditional way of life, dominated by agriculture, against soulless, imperialistic Yankee industrialists.
The Democratic Party slowly came to embrace the claims of African-Americans from the late 1940s through the 1960’s. They had a much better claim to “victimhood” than the southern whites, who consequently changed parties and became Republicans. As a result, both parties are largely controlled by groups who claim to be victims today. That is the principal reason our politics have become so vitriolic.