A look back on political party history
The Republican party hasn't changed nearly as much as the Democrats were. The Democrats bet the farm on slavery in the 1860s -- they wanted to protect it. They lost. So then they became the party of white power. Woodrow Wilson was incredibly racist for instance and undid many executive branch reforms brought in by Teddy Roosevelt and Taft. The KKK, the Jim Crowe laws, the seperate but equal schooling, seperate drinking fountains were all laws passed by Democrats over the objections of Republicans.
The first African American congressmen were Republicans.
But over time, overt racism is just a loser of an issue. Sensibilities change and Democrats like Woodrow Wilson and his contempoaries arguing that this country was for the white race sounded more and more ignorant and hateful. It was a lower of an issue. Of course, it took Democrats a long time to figure that out as Wilson was only one of two Democratic presidents since before 1860 (Wilson was elected in 1913 so picture only having 2 Democrats in office in a perid of 53 years).
So the Democrats found a new strategy -- rather than being the party of the white man they would become the party of the downtrodden.
The change began with the election of Franklin Roosevelt. He was earnestly trying to save the Republic but was also a shrewd politician. He was the first President to recognize the true power of the recently passed amendment allowing federal income taxes. He began teaching the masses, particularly the lower classes that democracy could be a tool in which they used the power of the ballot to confiscate the wealth generated by the upper classes. It wasn't hard given the inequalities of the time (people who argue that there are greater differences between the rich and the poor today than at any time in history are..to be charitable, wrong).
He was much more subtle and I believe more honorable in his intentions than later politicians would become. In those days (1930s to 1945) you could work hard and still be in poverty as millions of Americans of that era could attest to. I mean really working hard (full time working in a dangerous mine or mill or factory where you could die at any time and still be living in poverty). And people who cry about Enron should read up on the great depression in which millions of regular Americans suffered while a few percent of the elites walked away just fine.
So the earliest programs were about taking some wealth from the highest echelons of income earners and providing some benefits and services for those who were honestly trying to make their way in the world. Hence the term "New Deal".
Later Democrats recognized even greater opportunity by looking at the trends. Those who ended up being dependent on government help were overwhelmingly supporting them. No matter how well constructed, some percentage of people will always end up dependent on some goverment service. By pushing through programs that "assisted" the less fortuntae, they could create more and more dependents that would increasingly serve as their base.
And so here we are today with 90% of African Americans supporting the political party that literally fought to the death to keep them enslaved. Siding against the party that was largely formed (largely to free them whose very first President did free them (I'm not arguing that Lincoln was some sort of abolutionist, I am only arguing the facts here).
Democrats switched their strategy of white power to a strategy designed control of the less fortunate through the growing percentages of government dependents. Slaves of the government if you will. So I suppose, depending on how one looks at it, the Democrats haven't changed so much after all. They are still about keeping large segments of the population down in slavery. It's just that now they use much more flowery language to attain it.