This Sourcebook for Wraith: The Oblivion is an excellent piece of material. The book is well laid out with information useful to campaigns for the Wraith setting and is also a treasure trove of historical backgrounds as well.
Most of the Haunts in this sourcebook are overlaid on events that happened throughout history and actually taught me about an event that I had never heard of prior to this. I had my interest peaked on the last chapter about a World War II event that happened in Khatyn, Belarus. I did further research into the matter and found that the non-story elements (things not pertaining to the Wraith setting in particular) to be factual.
I highly recommend this sourcebook as it was quite inspiring to me in developing a portion of my campaign and gave me a great deal of insight into how the Underworld works.