the problems are not the physical boundaries, but rather the philosophical and ideological.
I am not sure if we will ever converge, barring much more wars and fighting. Ex. Israel. That situation will never be resolved peacefully. Though it may stale mate for a long time. Plenty of other examples. Religion and social customs are huge part of it, but so is governance strategy. Given enough time, enough failed states we may learn what is best, but there will always be some that disagree. Unless there is a dominant and ruthless ruling power willing to immediately to kill all dissidents. Though they would have to be very powerful to suppress all revolutions.
You could set up a single government, that allowed smaller divisions to self-govern, and could be geolocated based on shared political leanings & social customs, but thats not what you are asking.
Do you think people will evolve socially to the point to where they consider the quality of the lives of others to be as important as their own?
This counteracts our basic biology that puts our own survival and the survival of our families above all else. A human will NEVER care about a random human as much as they care for themselves and rightfully so. That would be devolution.