Susan Heitler, PhD, a private practice clinical psychologist and author, first became interested in parental alienation from working with a client whose distress stemmed from an alienation situation. 
Since that time Dr. Heitler has been helping to combat alienation by writing https://www.psychologytoday.com/intl/blog/resolution-not-conflict blogposts to educate psychotherapists, legal professionals, and the general public about the syndrome.  By the end of 2024 these posts had garnered over a million views.
For a list of these posts, see the Parental Alienation section of Dr.Heitler’s website, therapyhelp.com.

Note that in one of these posts Dr. Heitler extends the concept of alienation to what she refers to as Adult Sibling Alienation.  In these cases one adult sibling alienates an alienated elderly and often sickly parent from another sibling, generally in order to block that sibling’s access to an anticipated inheritance.
In other writings Dr. Heitler explains that alienation can occur on the macro level. For instance, Citizen Alienation occurs when leaders of one group or country turns their followers against a targeted other group or country via the spreading of false narratives.

Currently Dr. Heitler is aiming to extend the defining factors for parental alienation to include the spreading of false narratives about the targeted parent to others, e.g., to family members, friends and relevant professionals.