History 55,979 Indians of North America 12,625 Antiquities 10,343 Description and travel 8,415 National parks and reserves 7,346 Geology 6,462 World War, 1939-1945 6,311 more ... Park History Reports/Studies (Historical Documents) 5,697 Biography 5,349 United States 4,610 Management 4,459 Social life and customs 3,829 Politics and government 3,571 Paleontology 3,429 Environmental aspects 3,374 Campaigns 3,368 Excavations (Archaeology) 3,254 Frontier and pioneer life 3,175 Historic sites 3,087 Conservation and restoration 3,045 Planning 3,028 Juvenile literature 2,953 Natural history 2,946 Birds 2,662 Historic buildings 2,558 Pictorial works 2,391 Guidebooks 2,328 African Americans 2,317 Ecology 2,226 Regimental histories 2,190 less ...