> Members of tribes on tribal land have been subject to federal law since 1817, though crimes committed by tribe members against other tribe members on tribal land were within the jurisdiction of the tribes. So you had and have a system of concurrent federal and tribal jurisdiction.

From today's decision:

> 2) In Wong Kim Ark, the Court held that the Fourteenth Amendment was “declaratory” of the “fundamental rule of citizenship by birth” that prevailed at common law, 169 U. S., at 688, excluding only those recognized as exempt “from the jurisdiction of this country”—the“children of ambassadors” and those born in the nations of Indian tribes, id., at 675, 681–683, 693.

That's a 1898 decision where the status of native tribes was not at issue, but was used as an example. But it's roughly contemporaneous with the 14th amendment and shows why an Indian Citizenship Act would be needed.

Edited to add: There's also Elk v Wilkins (1884) which specifically held that Indians born on reservations did not get automatic citizenship.

Yes, but my point is that Wong Kim Ark is internally inconsistent. It doesn’t explain how the exclusion of Indians follows from its idea of what “subject to the jurisdiction” means.

Let me put it this way. What is a definition of “subject to the jurisdiction” that excludes Indians, other than saying “well, Indians aren’t included?” It can’t be “people who aren’t subject to US laws,” because Indians have been subject to U.S. laws since 1817, even on tribal lands.