• 1876 Supreme Court case ruled against any individual right to bear arms
• Second Amendment guaranteed only states' rights to maintain militias
• State governments could regulate guns however they saw fit
• Presser v. Illinois affirmed Cruikshank ruling, further clarified that Second Amendment rights had not been "incorporated"—that is, they were not binding on the states

Until quite recently, the answer to that question was pretty simple—the Court's interpretation of the Second Amendment was established in just a few cases. The first of these was United States v. Cruikshank. You can read more about this case here, but the short version is that in 1876 the Court ruled that the Second Amendment served only to protect the states against the federal government. Because the states in 1787 were worried that a too-powerful federal government might trample their rights, the Court said, the Second Amendment was added to the Constitution guaranteeing their right to maintain militias. The Second Amendment did not, in this interpretation, provide any individual right to keep and bear arms; it only guaranteed a state's right to maintain a militia. Moreover, since these militias were to be "well regulated," and since the Second Amendment was aimed only at the threat posed by the federal government, state governments were—according to this ruling—free to regulate guns in any manner they saw fit.

One of the critical holdings within the Cruikshank case was affirmed a decade later in Presser v. Illinois. This case stemmed from the arrest of a man named Herman Presser, who had organized military-style drills to train his own private militia of German-American workers, with the aim of fighting back against the armed security forces often hired by industrial employers. (Labor conflict in the late nineteenth century was a serious, and often violent, business.) The state argued that this sort of private militia was dangerous and illegal; Presser argued that it was protected by the Second Amendment. The Court ruled that the Second Amendment only restricted the federal government; it was not a prohibition against state action and therefore Illinois could regulate private militia. The Second Amendment, the Court ruled, did not give Herman Presser the right to run his own private army.

More precisely, Presser reaffirmed Cruikshank's conclusion that the Second Amendment had not been "incorporated" like some of the other amendments. The legal doctrine of incorporation states that the restrictions and demands placed on the federal government by the Bill of Rights apply selectively to the states as well. Even though initially these restrictions and demands were addressed only to the federal government, many have been extended to the states as well by the due process clause of the Fourteenth Amendment. The Fourteenth Amendment declares that the states may not "deprive any person of life, liberty, or property, without due process of law." The Court has held that many of the protections extended under the Bill of Rights are central to our understanding of liberty and therefore "fundamental" to the states' guarantee of due process of law.

Using this doctrine of incorporation, the Court has held that the states may not infringe on the freedoms of speech or the press; the Court has also ruled that the states may not restrict the freedom of religion, nor can they take actions that violate the separation of church and state. But one of the key points within this doctrine is that the Bill of Rights applies selectively to the states—that is, on a right-by-right basis. And—at least to this point in American history—the Court has never incorporated the Second Amendment. The rulings in Cruikshank and Presser continue to stand—the Second Amendment continues to be interpreted as a restriction only on the federal government, not on the states.

By the time the United States Supreme Court again took up the question of the Second Amendment in the twentieth century, certain things had changed. The states' militias had been converted into the National Guard, making them more fully controlled and funded by the federal government. The Second Amendment's guarantee to the states regarding their militias had subsequently lost most of its practical significance. But the Court continued to rule that the Second Amendment's protections were tied to military service and that there was no individual gun right independent of military service protected by the Constitution. Consequently, both the states and the federal government could legally impose regulations on individual gun ownership and use.