It is impossible to know the answers to these questions for certain. I would argue that the world is becoming more united, but that there is no way that we can ever live in perfect peace.
Some people might say that the world is becoming less united. We have terrible conflicts in the Middle East. We have conflict between the West and some of the Muslim world. There is tension between Pakistan and India. Other examples exist.
However, I would argue that the overall level of conflict in the world has dropped. There are still no serious tensions (that could foreseeably end in war) between the biggest countries of the world. The major conflicts in the world are either regional or intra-state. There is conflict between the West and the Muslim world but for the most part this is not conflict where governments are likely to go to war with one another. It is a conflict between the West and a certain group of radical Muslims. We do not have anything resembling the sorts of conflicts that led to the world wars or even the Cold War. Therefore, I would say that the world is becoming more united.
That does not mean, however, that I see a peaceful utopia in the future. Human beings appear to be too selfish, greedy, and tribal to allow for peace to ever become complete in this world.