World War I Centennial - National Archives
https://www.archives.gov/topics/wwi
As the largest repository of American World War I records, the National Archives invites you to browse the wealth of records and information documenting the U.S. experience in this conflict, including photographs, documents, audiovisual recordings, educational resources, articles, blog posts, lectures, and events.
World War II Photos | National Archives
https://www.archives.gov/research/military/ww2/photos
A collection of digitized World War II photographs from the holdings of the Still Picture Branch (RRSS) of the National Archives and Records Administration, including images from the Army Signal Corps, Department of the Navy, Coast Guard, Marine Corps, and Office of War Information.
Online Collections Database - National WWI Museum and Memorial
https://www.theworldwar.org/research/database
Explore the National WWI Museum and Memorial's online collections database, which allows you to search the digital records of their global collection that began in 1920. New digital records are added monthly, with a current focus on the museum's photograph collection.
1914-1918-Online. International Encyclopedia of the First World War (WW1)
https://encyclopedia.1914-1918-online.net/
The largest digital English-language reference work on the First World War, this multi-perspective, peer-reviewed, open-access knowledge base is the result of an international collaborative project involving over 1,200 authors, editors, and partners from over 50 countries.
World War I Collection - UNT Digital Library
https://digital.library.unt.edu/explore/collections/WWI/
Materials focusing on the World War I era from 1914 to 1918, including primary source documents, modern studies, and commemorative works. The collection includes photographs, posters, postcards, letters, and more.
World War II Collection - UNT Digital Library
https://digital.library.unt.edu/explore/collections/WWII/
This collection focuses on World War II and the immediate postwar period of the late 1940s, offering materials created during the time period as well as modern studies and commemorative works about the era. Includes posters, books, and more.
WW2 Archives – Free archives of the Second World War
https://wwiidigitalarchives.org/
This site offers free-for-download documents from the World War 2 era, with a focus on military archives. It is updated regularly with new files, hosting over 4,000 rolls and maps (more than 7Tb of files).
Library of Congress: Home
The Library of Congress houses vast digital collections, including extensive materials related to both World War I and World War II, such as posters, photographs, and historical documents.
Digitised First World War records - The National Archives (UK)
https://www.nationalarchives.gov.uk/first-world-war/centenary-digitised-records/
The UK's National Archives holds a vast collection of documents, letters, diaries, maps, and photographs from the First World War, many of which have been digitized and can be searched and downloaded online.