E.O. Wilson has proposed setting aside half the earth for nature. That would be achievable by protecting existing wilderness areas and connecting them together into corridors.

Which half ? Try to get humans to agree on it.

well realistically you only need to get the governments of the UN to agree which is a little less daunting. I can easily imaging taking the Sahara, Siberia, the interior of Australia, and the steppe would get us a good chunk of the way there. Adding on the amazon might be possible with effort.

Of course, these areas have substantial mineral/oil deposits that make the current political situtation difficult. But it's not outside of the realms of possibility that this may eventually stop being the case, such as how Britain's one ubiquitous coal mines are all closed now.

The thought experiment usually goes that the world's population could all fit into the state of Texas, at New York City density.

That always ignores the space required for agriculture, roads and transportation, waste management, power, manufacturing, and of course the natural resources that modern society depends on.

Also, I'd risk arrest or worse just to get out of that area and get some damn peace and quiet. I just spent a week in Chicago. It was fantastic. I'm really glad I'm not still there.

(And no, we shouldn't de-colonize Earth, we should get better at living in it.)