When you find materials that are on target, carefully observe subject headings. Click on those headings to do further searches. Repeat the process with more discovered headings as appropriate. Materials so described will help find additional materials, both primary and secondary. Once materials have been identified the footnotes and bibliographies contained in each will likely suggest primary resources that are available.
Some bibliographies separate primary and secondary materials.
Search for identified materials in the library catalog. Identify persons involved with the topic Using secondary sources, identify persons involved. The might be cabinet ministers, diplomats, rulers, eye-witnesses. Searches can be general or specific and use keywords or exact subject headings. New searches can than be created using either subject keywords or exact subject headings.