The Oxford English Dictionary defines Plagiarism as:
The action or practice of plagiarizing; the wrongful appropriation or purloining, and publication as one's own, of the ideas, or the expression of the ideas (literary, artistic, musical, mechanical, etc.) of another.
You must use citations when:
When in doubt, cite it!
Image Source: https://guides.library.utoronto.ca/citing
The joy of finding footnotes and bibliographic entries that lead to the perfect original source can only happen when scholars carefully track their sources and generate citations in an appropriate style. Neglecting to track your sources as you move through the research process will cost you HOURS of precious time.
Try this excellent tool: (click the image below)
Noodletools will not only help you create your footnotes and bibliography, it also will help you stay organized. When you create a project, you have the ability to record, link, and track your sources, attach notecards, make an outline, export a bibliography, and copy/paste footnotes into your paper. You also may share your project with your teacher and/or classmates.
For history assignments, you should use Chicago Style bibliography and footnotes, and choose the "advanced" option to get the most types of citation forms.