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- Population 30
- Demography 23
- Agriculture 11
- Politics and government 10
- Economics 8
- Hydrology 5
- Water-supply 5
- Labor 4
- Technology 3
- Urbanization 3
- Aquifers 2
- Armed Forces 2
- Bureaucracy 2
- Emigration and immigration 2
- Fertility 2
- Food 2
- Irrigation 2
- Rain and rainfall 2
- Reservoirs 2
- Watersheds 2