Traditionally feuds are over wealth, crown or other inheritances and are considered to be about money. Generally speaking, however, something deeper is going on, according to Psych Central in "Death, Wealth, and the Psychological Anatomy of a Family Dispute."
In the U.S., the participants in a family estate fight no longer enlist armies and fight it out on a field of battle. Instead, people today fight things out in Court. However, the reasons for today’s disputes are very similar to what they were hundreds of years ago.
Psychologists and even pop culture have known for a long time about sibling rivalry. Although there is disagreement about the core reasons for the phenomenon, no one disputes that it exists. Whether it has its roots in birth order, a desire to be loved more by parents or something else, sibling rivalry is a real thing that does not go away when children grow up.
The same psychological reasons that lead siblings to argue over who gets to ride shotgun in the car are the same reasons that lead to arguments over estates.
Knowing sibling rivalry exists and making estate plans with it in mind, can sometimes make for a smoother process.
Reference: Psych Central (Dec. 13, 2016) "Death, Wealth, and the Psychological Anatomy of a Family Dispute."