Studying modern history means that you my be using primary sources that are still under copyright law and thus not available full text online for free. This also means that there may be restrictions placed on depositories regarding digitalization. When choosing primary sources, please keep this in mind and plan accordingly.
Primary source research requires a slightly different approach to searching. Here are a few tips/strategies:
Start by doing some background reading or "pre-research": The more you know about key events, people, laws, and especially common terminology used during the time period you are researching the more successful your research will be. See the "Getting to Know Your Topic" page in this guide for help.
Limit to specific time periods: When searching for primary sources online always remember to use date ranges (usually on the advanced search page) to focus your search.
Use primary source keywords to find primary sources: Use search terms that reflect the types of primary sources you’re looking for, such as: diaries, pamphlets, correspondence, speeches, manuscripts, personal narratives, interviews, firsthand, eyewitness, sources, etc.
For example: slave AND diary | suffrage AND pamphlets | united states and race relations AND sources
The Library of Congress has a great tool for helping you evaluate potential primary sources: