Citations are absolutely essential in any academic paper, but particularly and especially in history. All information that is not from your own head must be cited, whether it’s a direct quote, a paraphrase, or even just an idea.
Citations are how we can tell the difference between what you’re claiming is your research and analysis, and the work of others. If you don’t cite others’ work, you’re claiming it for your own, and that’s plagiarism. Plagiarism is not tolerated at any academic institution; the lightest you’ll get off is a zero for the paper, but in many cases harsher penalties are invoked, including an F for the course and academic disciplinary proceedings that may result in a range of transcript-damaging punishments.
It is therefore crucial that you distinguish evidence you’ve gathered from primary and secondary sources from your own discussion, interpretation, and analysis. You do that with citations.
Having proper citations means making sure your paper has both of the following
- a bibliography: A list of the books and articles you used, and
- footnotes or in-text cites: which item in your bibliography a piece of information came from, plus a page number.
See the above links for more on how to make sure your papers are properly sourced and cited.