Quite importantly, he makes the distinction of nation vs. state.  It is a distinction worth internalizing for those who want to consider the application of libertarian theory in this world populated by humans.

From the interview, I learned of an essay written by Murray Rothbard in 1994, entitled Nations by Consent: Decomposing the Nation-State.  As is often the case, when I discover something of Rothbard's I find myself torn between excitement and depression: excitement because I have somehow worked my way to a conclusion similar to his, and depression because all I have done is somehow worked my way to a conclusion similar to his.

It is a quick read – ten pages.  I offer only a few highlights:

Libertarians tend to focus on two important units of analysis: the individual and the state. And yet, one of the most dramatic and significant events of our time has been the reemergence-with a bang-in the last five years of a third and much-neglected aspect of the real world, the "nation."

The "nation," of course, is not the same thing as the state, a difference that earlier libertarians and classical liberals such as Ludwig von Mises and Albert Jay Nock understood full well.

This "nation" is…culture:

Contemporary libertarians often assume, mistakenly, that individuals are bound to each other only by the nexus of market exchange. They forget that everyone is necessarily born into a family, a language, and a culture.

…usually including an ethnic group, with specific values, cultures, religious beliefs, and traditions.

To discuss the application of libertarian theory in the real world – a world made up of humans that are born into a family and culture – without recognizing this reality is nonsensical. Theory without recognizing human realities is a bad theory.

Rothbard goes on to the issue of political borders and suggests that God did not lay these down at the creation – there is no reason on earth to consider these permanent and sacred.  He doesn't write it this way, but this is what he writes.  Secession and decentralization and shifting political borders are both a historical reality and fully consistent with libertarian theory.

Rothbard explains when and why he began to rethink his views on immigration and open borders – he previously took the open borders position:

I began to rethink my views on immigration when, as the Soviet Union collapsed, it became clear that ethnic Russians had been encouraged to flood into Estonia and Latvia in order to destroy the cultures and languages of these peoples.