Adding the phrase based on a true story is more accurate.
There are some chilling tales about Nazi Germany, but it is not like it was in the movie... The movie changes the timeline to fit a movie versus what happened in the true story. The book would explain that better than I can.
The Von Trapp family did not have to escape from Germany, as shown in the film. They basically just immigrated to America, but had trouble getting permission to permanently stay in America.
Maria Von Trapp wrote a book about her experience.
Story of the Trapp Family Singers [Hardcover]1981
By Maria Augusta Von Trapp
ISBN-10 : 0397000189
ISBN-13 : 9780397000180
Publisher : Lippincott Williams & Wilkins
There is also a paperback version of the book published in 1957.