"Collapse" is in quotations because its definition when applied to civilizations is often debated.
Merriam-Webster's collegiate dictionary states:
1: to fall or shrink together abruptly and completely: fall into a jumbled or flattened mass through the force of external pressure 2: to break down
3: to cave or fall in or give way
4: to suddenly lose force, significance, effectiveness, or worth 5: to break down in vital energy, stamina, or self-control through exhaustion or disease; especially: to fall helpless or unconscious 6: to fold down into a more compact shape
Although this definition can vaguely describe the overall fall of most civilizations, the actual details are more finite. One such event would be an environmental change. Archaeologists use this as a reason for the decline of civilizations often because it fits so well into any situation. A terrifying earthquake, a change in flow of a vital river, and a volcanic eruption are examples of what could have happened to abruptly end a civilization. Another reason might be over use of natural resources. As civilizations grew, the need for more resources increased. They could not grow enough food to support the growing population, and as a result trade networks fell apart, people began to starve, and large epidemics spread. Also many of these civilizations based everything on ideology. They believe that their...