The Civil Rights Digital Library promotes an enhanced understanding of the struggle for racial equality in the 1950s & 1960s by helping users discover primary sources and other educational materials from libraries, archives, museums, public broadcasters, and others on a national scale.

The Digital Public Library of America (DPLA) is an all-digital library that aggregates metadata — or information describing an item — and thumbnails for millions of photographs, manuscripts, books, sounds, moving images, and more from libraries, archives, and museums across the United States. 

Access thousands of primary sources — letters, photographs, speeches, posters, maps, videos, and other document types — spanning the course of American history

The Library of Congress is the largest library in the world, with millions of books, recordings, photographs, newspapers, maps and manuscripts in its collections. The Library is the main research arm of the U.S. Congress and the home of the U.S. Copyright Office.

Google News has an option  to search over 100 years' worth of archived news from newspapers around the world.