One important consideration is that many of the larger countries are technically unified entities, but in reality they consist of many smaller governments with

One important consideration is that many of the larger countries are technically unified entities, but in reality they consist of many smaller governments with significant power (eg states in the US, Canada and India). They are tolerable because ultimately they still mostly recognize that people would rather be governed by an entity that has your local interests in mind, with the role of higher levels being to manage interactions between them. Thus, I don't see a world government happening until we're so well into colonizing other worlds that it's more practical to deal in terms of planets than with individual countries. Even at that point though, I'd expect something similar to countries to continue to exist. Put differently, I think a single entity with governance over the entirety of humanity is never going to happen (assuming we don't suffer some sort of near extinction level collapse).