History 88 Economic conditions 54 Politics and government 36 Science 29 Social conditions 27 Congresses 17 Geology 15 Economic policy 14 Periodicals 14 Agriculture 13 Economic aspects 12 Social sciences 11 Spanish language 11 Economic development 10 Education 10 Biography 9 Foreign relations 9 Land reform 9 Land tenure 9 Emigration and immigration 8 Research 8 Social aspects 8 Sources 8 Antiquities 7 Bibliography 7 History and criticism 7 Social policy 7 Working class 7 Botany 6 Colonies 6