As stated in the Library of Congress site, "Primary sources are the raw materials of history — original documents and objects which were created at the time under study."
For example: photographs of a protest march, a legal document such as The Constitution, the speech given by a famous person, a painting of a battle scene done by a witness, a letter from a king to another, an audio interview with a person who witnessed an important event, etc.
For example: an analysis of why the French Revolution changed the social classes in Europe, a book in which the author explains what happened during the battle of Agincourt, an article with someone's opinion on the influence of the "I have a dream" speech by Martin Luther King, Jr, etc.
750+ history reference books, encyclopedias, and the full-text of 60 history magazines. This database contains 58,000 historical documents; 43,000 biographies, 12,000 photos and maps; and 87 hours film and video. Funded by FLVC.
"Provides a complete overview of our nation’s past that covers the most-studied events, decades, conflicts, wars, political and cultural movements, and people. Comprehensive, contextual, media-rich information is provided on topics ranging from the arrival of Vikings in North America, to the stirrings of the revolution, through to the Civil Rights movement, 9/11, and the War on Terror." Funded by SCF Group License.
Covers every area of the world from the dawn of prehistory through the great ancient empires to the beginning of the Renaissance. Thousands of authoritative primary and secondary sources, in-depth explorations of key topics, and profiles of city-states, countries, and regions of the ancient and medieval world. Funded by SCF Group License.
Comprehensive overview of the emergence of the modern world from 1500 to the present. Covers Europe since the Renaissance, and concurrent developments in Asia, Africa, Latin America and the Islamic world. Funded by SCF Group License.