There are various synonyms for the phrase "cause estrangement". Some of these include alienate, distance, segregate, detach, disconnect, isolate, disunite, and break off. Each of these synonyms denotes a possible outcome of the act of causing estrangement, and they all have a negative connotation implying the breaking apart of a once close relationship. It is important to note that the act of causing estrangement is often irreversible and can leave a lasting impact on both parties involved. Therefore, it's wise to approach situations delicately and seek mediation to prevent loss of valuable relationships.