Did you know that as part of its mission to “promote the preservation and use of America’s documentary heritage,” the National Archives’ National Historical Publications and Records Commission (NHPRC - https://www.archives.gov/nhprc) has awarded digitization grants to institutions across the United States? Many of those institutions have made their digital collections freely available to the public, and they cover a wide range of topics, including the Civil War, environmental activism, social welfare, civil rights, agriculture, advertising, and much more!
Here are just a few examples of the variety of digitization projects made possible by the NHPRC:
The University of Iowa digitized its Henry A. Wallace collection. Wallace served as the Secretary of Agriculture from 1933-1950, as the Vice President from 1941-1945, and as the Secretary of Commerce from 1945-1946. You can view this collection here: http://wallace.lib.uiowa.edu/
The Auburn Avenue Research Library on African American Culture and History, which is part of the Atlanta-Fulton Public Library System, worked with the Digital Library of Georgia “to digitize and make Web-accessible late nineteenth and mid-twentieth century manuscript collections that document the historical development of education for African Americans, primarily in the South, from the early 1860s to the early 1950s.” Check out their collections here: http://www.afpls.org/aarl
The Aldo Leopold Foundation and the University of Wisconsin at Madison digitized their Aldo Leopold collection. Leopold, the author of A Sand County Almanac (1949) was--among other things--an American environmentalist and forester. You can view the collection here: https://uwdc.library.wisc.edu/collections/aldoleopold/