At some point in time the truth is illuminated and the practice of Dhamma flourishes. As time goes on and generations pass away the practice degenerates until the Teaching fades away completely. After a time the Teaching is re-founded and flourishes once more. As time goes on the adherents of the Dhamma multiply, prosperity sets in, and once more the Teaching begins to follow the darkness of the world. And so once more it degenerates until such a time as it can no longer hold ground.
Confusion reigns once more.
Then it is time to re-establish the truth. In fact the truth doesn't go anywhere. When Buddhas pass away the Dhamma doesn't disappear with them. The world revolves like this. It's something like a mango tree.