Consider referencing a reputable history book or established websites, like those from the Library of Congress or educational institutions. You can incorporate citations directly in your text for clarity, such as saying, "The Louisiana Purchase occurred in 1803 (Smith, 2020)," which provides the necessary citation without undue emphasis. General history books covering the relevant era can also serve as valuable references, for instance, "As discussed in A People's History of the United States by Howard Zinn." Additionally, entries from encyclopedias, like Britannica, are useful for straightforward historical facts, such as stating, "The Louisiana Purchase, according to the Encyclopedia Britannica, occurred in 1803."

I agree with Magallón and think that, as a general rule, we should prioritize the originals, i.e., those who first recorded the subject or discovery. Regards, Valdo

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Yes, pointing generally to standard literature (the earliest, the most comprehensive) is a good idea.

Quoting established encyclopedias is possible, but maybe superfluous. Because it may also be allowed to provide no citation at all, if it is about obvious and undisputed facts which do not contribute much to the point you want to make in your thesis.

In the end, citations are there for helping the reader to understand and verify your point. Less can be more, sometimes.

Even if the subject is known in History, I prefer to give two or even three references on this subject. These multiple references confirm the importance of the event, show young historians that references are the basis of History and give the seriousness and fidelity of the truth.