The world cannot never be united unless there's 1 world government and borders are removed.
Yes countries wont agree with each other however if all countries use the same systems & infrastructure for example systems/infrastructures networked via the internet where the tyrant country now has the opportunity to impose its will on the world not by force like wars but via a system reset where it crashes everything that was built on the internet that took decades to build lets say like the 'Die Hard 4.0' movie where the Reset is planning to happen and if succeeded it will force all countries to start new and fresh with the Agenda the tyrant country wants in the world.
Possibility? Because everything is run on computers & Internet nowadays in the world including financial markets like the stock markets & even Bitcoin!
Not related to topic...Just popped to my mind, but do you see a possibility that when every country explores space (given we have a ship that can travel at warp speed) and set up there country in one planet and every other country will do the same? And space wars and planetary invasions will occur by who the powerful nation/planet is? And may be humans are the only species in the universe that killing each other and not united?