You know John Green as the author of some pretty good YA books, like The Fault in Our Stars, Paper Towns, and Looking for Alaska which have been living on the NY Times YA Best Sellers list for more that 106 weeks. Green has won a number of awards for his books, and in 2014, was named one of Time magazine's 100 most influential people.
In 2012, after receiving a grant from Google, Green and his brother Hank began a series of educational videos on YouTube called Crash Course. Green gives crash courses on World History, American History and Literature, while Hank covers Biology, Chemistry, Ecology and Psychology.
Here are the three Crash Courses that John Green did on WWII. Each is approximately 13-15 minutes long. They really just introduce you to the topic, so don't expect in-depth detail, but they are interesting and informative.