Different historians have come up with different causes for the collapse of civilizations. Sort the effects based on whether they were caused by overpopulation, drought, or both.

Collapse of a government bureaucracy.

Food shortage.

Mass migration.

Water shortage.

Pollution of water.

Economic collapse.

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.