Scholarly academic journals offer relatively short examinations of very specific historical documents or events. You can search using keywords in either a single scholarly journal, or a scholarly database that lets you search hundreds or thousands of academic journals at once.
Scholarly databases tag together articles on specific topics using subjects. If you find a single article that looks relevant to your research topic, check the subject tags and click on them to search for similar articles. There are also a few journals that focus specifically on the history of colonial Latin America.