Economic aspects Agriculture 284 History 178 Economic conditions 164 World War, 1914-1918 140 Social aspects 65 World War, 1939-1945 60 more ... Agriculture and state 52 Social conditions 52 Education 39 Pollution 39 Slavery 38 War 36 Economic policy 34 Politics and government 31 Rural conditions 31 Population 30 Environmental policy 27 Finance 24 Race relations 24 African Americans 23 Food supply 23 Technological innovations 23 Land tenure 22 Commerce 21 Emigration and immigration 21 Government policy 21 Political aspects 20 Industries 19 Peasants 18 less ...