How do you punish the founder of a slave empire?

On today's walk I was thinking about how one could appropriately punish the founder of a slave empire, such as Jefferson Davis. I felt complete outrage how Jefferson Davis and Robert E. Lee, along with the members of the Confederate Congress who did not receive any punishment. This felt like an absolute injustice to me when thinking of how many years we send people to prison for in terms of

My first response was to try to match the punishment to the crime (enslavement of millions of people) on the leading generals, congress, and administration of that slave empire. Under a system of making the punishment fit the crime, I got a little creative of my ideas of how to punish them. My first thought would be to draw out their intestines as the fascists lie in the mud, bleeding but not enough so that they die in unimaginable pain, after which they would be hung until they bleed to death slowly.

I then thought this was too humane. They must not be killed, they would have to absolutely suffer to match the level of pain they caused to millions of African Americans. They would need to work every day of their lives with no break and be whipped multiple times every day. They would only be given enough food to survive, to make the suffering last as long as possible. This would simulate the situations they forced on people, and fit the Hammurabi code. It also matches the treat others as you wish to be treated value which is essentially the same idea.

On the other hand, this is Rule of Man. Rule of Man is problematic because of the slippery slope it leads to totalitarian government. The punishment for their crime would then have to be as dictated by US Code. The punishment would then have to be as dictated by law.

Another issue then becomes whether it would prevent future crimes, and the research demonstrates that such extreme punishment does not deter future crimes. In order to fully end the problem one would have to look at the root causes of what caused these people to commit such a horrendous crime, and then address those directly to improve the lives of former slaves. This would be a system of programs which end the racism and improve the economic well being of former slaves, like what Presidents Franklin Delano Roosevelt, Harry S. Truman, John F. Kennedy, and Lyndon Baines Johnson passed in their presidencies which struck at the underlying economic and social causes of the impoverishment of African Americans. Fighting people's attitudes about slavery however is the hardest step of all, and I still don't know how to effectively combat racist attitudes at a massive scale, which is probably the biggest gap in education at this point in time.

If your goal is deterring crime, complete revenge matching the severity is not the solution, and the best way to fully punish the leaders of the Confederacy would have been a continuation of Reconstruction after 1877 when Rutherford B. Hayes stepped into the White House. The best way to punish them is to continue the work of ending racism, which will put their ideology where it belongs which is the dustbin of history. This prevents the creation of them as a martyr and punishes the crime more than the individual which is what the real goal should be.