Especially for these informative essays, for almost everything you write in an academic paper it's assumed the information came from an outside source. No one is born with innate knowledge of world history, science or social engineering. If you have knowledge about this without reading a book, watching a movie or hearing a lecture it's because you have probably done one of those things in the past.
Where this gets tricky is when you have knowledge from years ago that you want to write about. In the strictest sense, if you learned it from a source years ago you should cite it. Now most people don't keep a bibliography of their lives so the other option is to find a source that says the same information. I suggest this for two reasons. You avoid the suspicion and the potential for plagiarism. And two you give your writing validity and strength by linking your thoughts to other knowledgeable people.