How would have D.W. Griffith influenced a movie such as Casablanca?
Not directly, but the basic grammar of film — the way narrative and meaning are conveyed through camera movement, editing, and montage — is something Griffith pretty much invented. So 30 years later, “Casablanca” director MIchael Curtiz would have been using the same or similar techniques, even if he wasn’t consciously thinking of Griffith’s movies when he did so.