The world of Karma and Despair

For a long time, the people of this world have believed that they know all that is to know of the world that they live in. How could they not, they have explored every corner of this world. And are believed to be at the peak of their civilization. However, just like any civilization ever created there will always be a decline, and what if the cause of this decline was not of this world. The past will always catch up one way or another.