Historians publish books and journal articles, so be sure to look for both when doing research in history.
QuickSearch searches books and articles at the same time, so it is always a good starting place for your topic.
If your search results are overwhelming or not as relevant as you would like, it might be time to try a specialized database.
America: History & Life helps you find articles about the history of the United States and Canada published in history journals.
If you are looking for articles about the histories outside of North America, try Academic Search Complete. This is an interdisciplinary database, so it will include articles from other fields. However, if you add "History" to your search as a Subject Term, you should get more focused results written mostly by historians.
Note that I have put the phrase "Jesuit missions" in quotation marks. This causes the database to search these words together, as a phrase, rather than two separate keywords. This technique is especially useful when searching multi-word names like "United States" or "United Kingdom" where the words united, states, and kingdom may show up in other contexts and return irrelevant search results.
JSTOR is another interdisciplinary database with lots of full text journal articles.
Searching JSTOR is a bit different from the history databases mentioned above.
Pro Tip: JSTOR is interdisciplinary, but you can limit your results to only include articles from history journals. With JSTOR's Advanced Search, enter your keywords, then scroll down to the Journal Filter section. Check the box next to History and your results will only come from those journals listed in the History category.
Some databases not only specialize in history, but also in specific regions or time periods. Choose one of these databases if you are doing research in one of these subfields of history.