In Christian circles, the term "postmillennialism" refers to an optimistic view of human history according to which the kingdom of God will be fully established after a long period of time, or millennium, of gradual improvement. The term "premillennialism" refers to a pessimistic view. It holds that things will dramatically worsen and the Second Coming of Jesus will occur before the millennium. Although each group tends to isolate itself from the other, sometimes they encounter and dialogue with each other about this issue
One of the things that besets these conversations is the tendency to think that if a person is not one of these he or she must be the other. This is not so because there are the "amillennialists" who think that both of these two positions are too literalistic and insufficiently sensitive to the degree that the key concepts may belong to a different and non-temporal sphere of things.
There is a different problem with both postmillennialism and premillennialism and this is that both often suffer from the "fallacy of inevitability." The first group is persuaded by divine goodness that all things cannot help but improve. The second group is convinced by human badness that all things cannot help but deteriorate until the Second Coming of Christ rescues the situation. Members of both groups can be disappointed, despondent or even despairing when the "signs of the times" are not what they anticipate.
It is doubtful that all things will get either better or worse. It is far more likely that in the future some things will get better and some things will get worse. That's seems to be the way things have been going for a very long time.
It is also doubtful that there is anything inevitable about the future of humanity. Nobody can predict in any detail what is going to happen in the next day, week, month, year, century or eon and the further we look into the future we look the less accurate our predictions are likely to be. Much depends upon what we choose. As Scripture says, we can choose life and we can choose death. Our choices are constrained but genuine and how we make them will help determine what the future will be like.
An optimistic view of the future of humanity is false. So is a pessimistic one. More precisely, they are both mistaken to the degree that they commit the fallacy of inevitability. Because human history is partly up to what we choose, our view of humanity's future should be neither of these but voluntary.