I fully recommend to all gaffers to go and watch BBC documentary "The Great War" from 1964. In-depth 26 episode long look at the entire war, fought pretty much because Germany wanted it badly enough.
Ep1 http://www.youtube.com/watch?v=fXhiagFG8KE
BBC's next documentary "World at War" which detailed WW2 is even better.
Is World at War narrated by Laurence Olivier? If so, it's available in the US on DVD on netflix. The Great War doesn't seem to have ever gotten a US release.