History 54 Congresses 29 Politics and government 21 History and criticism 17 Economic conditions 16 Education 10 Social conditions 9 Biography 8 Foreign relations 8 Employment 7 Afro-Americans 6 Collective bargaining 6 Criticism and interpretation 6 Commerce 5 Data processing 5 Mathematical models 5 Philosophy 5 Prices 5 Research 5 Social aspects 5 Social life and customs 5 Study and teaching 5 Wages 5 African Americans 4 Agriculture 4 Bibliography 4 Civilization 4 Economic aspects 4 Economic policy 4 Economics 4