My boyfriend was a history major but he's not been particularly helpful in this case. The scope of my topic has to be from 17th century to present. I took out a bunch of books from the library and I'm still trying to narrow it down, but I think I'm mostly confused on what historical research papers are supposed to argue. I want my topic to be on something related to female scientists. Something along the lines of how they were treated compared to male scientists, how seriously (or not) they were taken, or maybe something along the lines of how women scientists were treated in different regions of the world.
But I just don't know how to construct a thesis. I don't know what a historical research paper is supposed to argue. My boyfriend told me it can't be a compare and contrast but I just... I don't know what sort of things I'm supposed to argue! Please help me.
It sounds to me like you already have some solid questions that will provide a good starting point (how were female scientists treated, how seriously were they taken, etc.). Begin there, read everything that you can, and pay attention. As you read, you'll start to answer some of your initial research questions, which will lead to further questions. What patterns do you notice? Is there something that jumps out or is there a common theme that runs through what you read? Maybe there an angle that you notice that other authors don't seem to mention? Make sure to take copious notes, as these will come in handy later.
As you learn more, you may find an angle you are more interested in, or you may come back to your original question i.e., how were female scientists treated? The thesis or argument of your paper will be your answer to your research questions, supported with the information and other facts you have gathered. In other words, you will make a claim and support it; "women were treated in 'x' manner(s); here is the evidence to support such and such claim(s)" --hopefully a little more articulate than that though :)
I'd also advise you to narrow down the scope of your project. But if the requirement is to cover 400 years of history, focus on a particular region or culture. Comparison papers aren't a bad thing, and if you're to cover that much time, you will be doing a comparison paper anyways (how were women treated at different times throughout history) and drawing conclusions about what those changes mean or why they are important. There's nothing wrong with cross-cultural comparisons though, but you will need to clarify and argue why such a comparison is valid or relevant. A laundry list of similarities and differences is not an argument.
Above all though, ask your professor, get his or her advice, and bounce some of your ideas around. That's part of the reason why he or she is there-- especially if it is an introductory course, as the point will be to teach you how to write history and construct an argument. I don't know the specifics or details of the assignment after all. My advice is to go to the source if you have a serious problem with how to construct your argument.