Final answer:
The two issues that often contribute to the fall of civilizations are problems from within and D) outside invasions, with factors like climate change, disease, and warfare playing significant roles in the historical collapses.
Step-by-step explanation:
The two issues often contributing to the fall of civilizations are problems from within (such as political, economic, or social instability) and outside invasions by other civilizations or nomadic groups. Civilizations are complex entities, and their demise can seldom be attributed to a single cause. Throughout history, many factors such as climate change, disease, and warfare have played significant roles in the collapse of various societies.
For instance, the decline of the Ottoman Empire was partly due to financial troubles, while the Mycenaean civilization fell after a combination of climatic events and invasions. Similarly, the Bronze Age collapse was a result of environmental catastrophes compounded by external threats such as the Sea Peoples' invasions. The general pattern suggests internal strife and external pressures often combine to precipitate a civilization's fall.