Provides citations to books and other materials (including those that are out of print) held by libraries worldwide and allows users to request books via Interlibrary Loan. *This resource is provided by the Electronic Library of Minnesota, freely accessible to anyone in Minnesota!*
Specialized encyclopedia's provide excellent introductions to topics and can introduce you to important research on the topic.
Library Services has both print and online encyclopedias for US History topics. They can all be found in MavScholar. Here are a few examples.