The first big case on substantive due process is Munn versus Illinois in 1877. It seems pretty clear that the reason you have the expansion of substantive due process in 1877 is because of the death of the Privileges or Immunities Clause four years before in Slaughter-House in 1873. In Munn, the Court says there is an important core of substantive rights protected by the Due Process Clause. The Munn court takes a distinction made 200 years before by Chief Justice Matthew Hale. Matthew Hale distinguished between three kinds of areas of the law. We have the ius regium, which is things that the government itself is doing. We have the ius privatum, which is things that purely private people, with no public interest involved, are doing. But in between there, you have things that people like the railroads or grain elevators are doing. That's the ius publicum. So, these are businesses that are affected with a public interest. So, what Munn says is that, if you are in the ius publicum, you can be subject to a duty to serve all members of the public equally. We can have regulations of businesses affected with a public interest if those regulations serve the public good. But due process prevents the government from regulating people who are merely in the ius privatum. The Court in Munn gave, really, no textual explanation for why the Due Process Clause should be accomplishing this end. There's a much, much better argument for saying that to be a citizen means the right to mind your own affairs under the ius privatum, and also the right to be treated as an equal when you're dealing with businesses in the ius publicum. In 1872, the discussions in Congress make clear that the common law tradition of these sorts of distinctions is seen to be baked into the Privileges or Immunities Clause. So, you can justify the doctrine that they come up with in cases like Munn much more easily under the Privileges or Immunities Clause. It seems pretty clear that the reason they put that into the Fourteenth Amendment is because they really realized, by that point, that they should have been using the Privileges or Immunities Clause. They shouldn't have killed it prematurely in 1873. But they think, "Oh, well, we can just use the Due Process Clause instead." Given that Justice Strong himself was saying that there should be substantive rights, it seems like the coalition, to say there should be very few substantive rights under the Fourteenth Amendment, had fallen apart.