O death, where is thy sting? O grave, where is thy victory?
Actually, the world is a BETTER place than ever in history. Statistics can show that clearly. And it is that way because of the slow erosion of the effects of sin that were perpetrated on the world by the devil. Now that he is gone, and Christ is on the throne of the universe, more people than ever daily enter the gates of Christ's kingdom.
You are caught in the classic trap of being in a small slice of time and comparing your own experience and view with that of history.
I am convinced that God takes the long view of things, and this promise of healing is actually happening every moment of every day. However, don't expect to see details of it on CBS Nightly News. Instead, take a visit to the local soup kitchen, or the battered women's shelters, of the countless ways people interact and show kindnesses to one another. THAT is the healing of the nations.
Remember too that the last book of Revelation says that outside the gates are the sinners, and they have no right to eternal life. But INSIDE the gates are where the healing is going on. If you look outside the gates, you will indeed see the results of the sins of generations being spent on the nations. Only those who enter into the gates will experience the healing of the leaves. There IS a balm in Gilead, and it heals the sin sick soul.