Search strategy: Once you have found a few excellent articles on your topic, a great next step is to look at the citations associated with those articles. You can look backward and forward.
Backward: Take that excellent article and look at the references the authors used when conducting their study.
Forward: You can also look at who then used the article at some future date for their own research. This makes sense when the article is a bit older. Who cited the article in their own research?
This type of citation searching looks forward in time. It is sometimes called the descendancy approach (because it searches forward from a descendant). It starts with a historical article, and searches for articles that were written AFTER the historical article -- ones that used the historical article for research.
How many times has a historical article been cited since it was published? A historical article may continue to be cited for various reasons. Often it is because it was an important or influential article, a seminal article, one that established a theory or reported on a significant research discovery. While those are typical reasons that an article endures, another less common but possible reason may be that the article is controversial and it is for that reason it is often cited.
This type of citation searching looks backwards in time. It starts with an article, often a fairly recent one, and looks back at the articles in the reference list. It is sometimes called the ascendancy approach (because it searches backward from an ascendant). It starts with a current article, and searches for articles that were written BEFORE the current article. These articles were used by the authors when conducting their research on the current article.