There are some fantastic sources for documentary and historical footage out there, including my personal favorites: turn of the century films from the dawn of the cinematic era.
Thomas Edison’s company was in the forefront of filming current events — from relatively banal but riveting-in-hindsight scenes of 1900s New York City, to the wreckage of the USS Maine in Havana Harbor (see pic below). According to the Library of Congress — which has an extraordinary collection of Spanish-American War film — the demand for war footage was particularly acute, although technological limitations made actually filming battle scenes virtually impossible. Enter the bread and butter of the History Channel: the historical reenactment.
Check out the Library of Congress’ other early film collections here.