Economic aspects Agriculture 284 History 176 Economic conditions 165 World War, 1914-1918 140 Social aspects 63 World War, 1939-1945 60 more ... Social conditions 53 Agriculture and state 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 Food supply 23 Race relations 23 Technological innovations 23 African Americans 22 Land tenure 22 Commerce 21 Emigration and immigration 21 Government policy 21 Political aspects 20 Industries 19 Peasants 18 less ...