If the Recommend Historical Collections don't provide you with what you are searching for, you can try the sources listed in the subpages. The sources listed within the subpages are loosely grouped by subject.
About the Source Websites (Interfaces)
Each of these sources will have a different interface. Some are designed better than others. If you feel overwhelmed by what you see, take some time to learn about the website. Most will provide you with tips about how to search for information. It will be helpful to start with broad keywords and narrow them down once you see your initial search results.