The idea behind How Film Became History was to trace the origin of the motion picture genre that is now the central repository for our shared history--the archival documentary. 

“Films beget films,” declared the film historian Jay Leyda, but only in the 1930s would they become fruitful and multiply. The proliferation was due to two parallel developments, one archival, one technological. By 1930, a sufficient backlog of motion pictures—roughly four decades worth of filmed life—had accrued to provide the raw material to spawn a second generation stitched together exclusively from the first.  That same year, Hollywood completed the task begun in 1927, the re-tooling of the studio assembly lines for the recording of synchronous dialogue.   Together, the accumulation of a film inventory and the sound of the human voice gave rise to a new motion picture genre. 

“Archival documentary” became the term for the branch of next-generation cinema, though the name would not stick until the end of the twentieth century. In the 1930s, the decade in which it came of age, critics and practitioners struggled for the right label: compilation films, library films, historical films, salvage films, celluloid anthologies, synthetic features, episodic reelage, super newsreel, and collections of stock footage. Whatever the name, it referred to a parasitical genre that drew its life from pre-existing film.  

By 1930, plenty of source material had grown up to feed the new format.  After the Lumière brothers turned on their projector, the production of motion pictures accelerated as fast as the cellulose nitrate film stock could be processed.   

But if the accumulation of some forty years of film footage was a necessary precondition for the creation of the archival documentary, the introduction of synchronous sound into the grammar of cinema was the decisive addition—soundtrack music, ambient noise, and, above all, the human voice. Joined together, the commentary from the human voice and the backlog of film footage parented a supple new medium for the transmission of history.