The correct matches are:
Collapse of government bureaucracy - Overpopulation
Food shortage - Both
Mass migration - Both
Water shortage - Drought
Pollution of water - Overpopulation
Economic collapse - Drought
The collapse of the civilizations is a theme that is still debatable, as there's still no definitive answers for the collapse of lot of civilizations. The overpopulation and prolonged droughts though, seem to be the main causes in general.
The overpopulation leads to lot of problems, as the society is existing on the limit of the resources available, so only a slight problem can cause a disaster. A prolonged drought can be fatal, as the water will be reduced, and there will be lack of food. That will naturally lead to revolt, the rulers overthrown or abandoned, and the people will move in large numbers in other ares where they will have food and water. That in turn will result in the fall of the government bureaucracy, as there will be no people left to rule over.
