I don't know how long this feature has been available but I just noticed it. The Facts on File main page now has a federated search engine. It's on the right side of the screen and called "History Database Search". Using this search tool, you can select to search across America History Online, American Indian H.O., American Women's H.O., African American H.O., Modern World H.O. and Ancient and Medieval H.O. That's pretty helpful! It allows you to perform a basic or advanced search as well.