Perhaps you're forgetting the most obvious influence...

Rating: Null/10 (13 November 2003)

The most obvious influence for this movie isn't a movie, it's a book. Conrad's "Heart of Darkness". Kurtz is the same character in the movie and in the book, and Willard represents Marlow from the book. Even the character played by Dennis Hopper comes from "Heart of Darkness". The book is about the colonization and exploitation of Africa by the Europeans in the late 1800s. The setting is on the Congo river, and they travel up the river closer towards "Darkness" or Kurtz. This is the same paralell as the river in Vietnam depicted in Apocalypse Now. I thought the movie was great, and much easier to stay involved with than the Stream of Consciousness writing style that is present in Conrad's Heart of Darkness.