Because each senior thesis is so different, this page offers only a few starting places to search for primary sources. Rather than sharing direct links to digitized primary sources on every historical topic imaginable, the focus is on tips and tricks for your own internet searches. If you would like a personalized round-up of a handful of primary source collections relevant to your topic, your librarian is available to provide that upon request. Just email reference@puc.edu.
This is a brief list of digital collections made available by national libraries, primarily in English speaking countries. Obviously, there is much, much more available online. Use this as inspiration or a starting place, or jump right down to the bottom of this page for my tips to find digital collections for yourself.
I am about to reveal my secrets to you. This is my magic Google move that finds collections of primary sources that have been digitized and made available freely online.
For visual learners, here is the process I just described.
1. I choose broad keywords.
2. I add another keyword like "archives."
3. I search Google and begin to assess my results.
4. I continue to assess my results, selecting a link to study further. I choose the third link here, because I see that the URL ends with byu.edu, which means it is a page hosted by Brigham Young University. Although universities can have agendas and biases, they are also known for academic freedom and generally unbiased research, so if this page looks alright once I open it, I can probably trust it. As you can see from the screenshot below, this page is a roundup of links to digital collections that BYU recommends to its students. I will click the first one to see if it contains a trustworthy online collection worth browsing.
5. The first link here belongs to a library and archive dedicated to the history of German-speaking Jews. I know this because I visited the About page. I trust that this repository will share digital collections that have reliable and correct metadata (descriptions of the documents, photographs, etc.). I am willing to search this source with more targeted keywords to see if I can find primary sources relevant to my project.