How will America end?

All great empires have come to an end and I doubt America is any different than any other dominate people in world history.  Assyria was crushed by a superior military force, Babylon fell when an enemy found a weakness in their defense system, and Alexander the Great's kingdom fell prey to the Romans when his kingdom was divided among his generals.  The Roman Empire fell because of its decadence
   The Roman Empire ruled the world for over three hundred years and at the time of it's collapse was still the greatest military power in the world.  The empire had come apart at the seems politically and society was collapsing in upon itself because of moral decay.  It was as if Rome was a fine piece of clothing that had been sewn together with cheap thread and as the fabric aged the cloth became brittle and the thread rotted and the piece of clothing just crumbled.
  It seems that there is a pattern to the growth, stability, and eventually collapse of each of the world's greatest empires and America fits that same pattern.  Will it be the Russians that take America down, the Chinese, ISIS. or some unknown force that has not come to the forefront yet?     In my opinion it will be none of these.  America will be toppled from within and not from some outside force.
  Our liberal immigration policies are allowing enough people into this country, some who want to change America, some who want to destroy it, and many others who just want to take advantage of us.  We seem to have forgotten what made this country great and has allowed the attitude of respect for the beliefs of others to disintegrate into embracing and accepting everyone as they are.  I think that we will lose our national identity     and no longer know what we believe in, becoming a nation of divided factions  each of which wants to live their lives after their own beliefs rather than living their lives for the benefit of the majority.  A house divided against itself cannot stand.