Use the Library's Catalog Advanced Search to find primary sources on your Ethnohistory topic in the WMU collection.
Since the terms "primary documents" or "primary sources" are not Library of Congress (LC) subject headings, these are not the best keywords to use. Try some of these keywords instead:
The trick is to combine one or more of these keywords with whatever topic you are researching. For example:
or the following search:
While not every single item that comes up is guaranteed to be a primary document, at least some of them should be.