Why wasn't WWI talked about in America: The Story of Us on History channel?

I've seen every episode on the America: Story of Us program on the History Channel and I love it and find it very entertaining. I know it's trying to cram hundreds of years of history into a mini series..but WWI was pretty big. You would think all the major wars would be covered. I haven't really heard anything about WWI. It went from the Industrial Revolution and Prohibition straight into the Depression and WWII....?? Why is WWI missing?