Final answer:
The decline of civilizations such as the Indus Valley civilization and the Classical Maya civilization can be attributed to a combination of factors including environmental degradation, disease, and invasions. These civilizations experienced a decline in population and the breakdown of their societies.
Step-by-step explanation:
The decline of the Indus Valley civilization may have been caused by a combination of factors including environmental degradation, climate change, disease, and invasions. Environmental degradation caused by resource exploitation and population density likely weakened the civilization. This could have been worsened by climate change and disease, making the region more vulnerable to attacks by raiding groups.
The decline of the Classical Maya civilization is also attributed to various factors such as epidemic diseases, invasions, natural disasters, internal revolutions, and environmental degradation. It is unlikely that a single cause led to the collapse of the Maya civilization.
Similarly, the decline of other civilizations throughout history has been influenced by factors like climate change, disease, and warfare from neighboring civilizations. However, the collapse of civilizations also presents opportunities for new civilizations to emerge.