I do not have time to read many books these days. But I managed to finish "Children of a modest star" (Jonathan S. Blake and Nils Gilman), which was highly recommended by a review in Science: https://www.science.org/doi/10.1126/science.ado2345. (The title is from a poem by W.H. Auden.)
I would say that it is about political theory, or political philosophy, but the authors draw on their extensive knowledge of intellectual history. They argue that the idea of the nation state as the main container of sovereignty is a fairly recent idea that is already under attack. This idea appealed to me because I have written a fair but about the vices of nationalism and the virtues of cosmpolitanism. But the book goes beyond this polarity by arguing for a principle of "subsidarity", which holds that problems should be handled by the lowest political subdivision capable of handling them, which is often sub-national. It still argues for a "planetary" level of government, with enforcement power, as necessary for such issues as climate change, preparedness for pandemics, and biodiversity. It is not, and does not claim to be, a fully worked out plan for how things would work in the future it proposes. It presents a rough vision of where we should be headed, and even how we might get from here to there.
Within the community of card-carrying utilitarians, I have been suspicious of "longtermism" as recommended by William MacAskill and others. It is too easy to come up with some fantasy about the long-term future, like that of one person I knew who argued that practically all of our extra resources should be spent trying to find ways to stop a large asteroid from hitting the earth, since, if we don't solve this problem, it is inevitable that this will happen eventually. (I think that we humans now have the capacity to deal with this problem, although I don't know how large an asteroid we could deflect.) Thus, I have thought that the most sensible utilitarian approach to government is to look for incremental improvements in the situation, without worrying too much about their long-term effects, which are difficult to predict. It makes sense to reduce CO2 emissions even if it turns out that, in a few decades, we will use fusion power from a single site to pull CO2 right out of the atmosphere.
Still, I found the book an answer to the question: If you want to consider the long term future, what aspect of it is most relevant? The answer is to look at effects on governance.
The prose is incredibly good. Almost every page has something you put on a t shirt. Although you can read through the 215 pages of text as if this were simply a political manifesto without much anchoring in prior literature, it has 69 pages of footnotes at the end. All the ideas are credited to writings that inspired or preceded them.
