We tend to think of families as all getting along and supporting and protecting each other. For most families in the Middle Ages, that was probably the norm as well. But just as today siblings can become very competitive over such things as "who gets Grandma's gold coin collection," so among the medieval aristocracy there was often fierce competition between brothers.
This is to be anticipated, because even though there were no strict rules of primogeniture (that is, of the oldest son getting everything), oldest sons did tend to inherit more, and the younger sons thought this was Totally Unfair. Throughout the medieval and early modern period there were plenty of tales about three brothers, where the oldest gets the big inheritance, the middle one gets some small thing, and the third is told, "Good luck, kid." Of course in these stories the youngest heads off and finds something worth far more than the original inheritance, and even a princess to marry. Take that, older brother!
The Merovingian kings of what is now France (fifth to eighth centuries) were described by contemporaries as ready to slay their brothers and cousins. The various small kingdoms, into which what is now France and the Low Countries were divided, were parceled out between heirs, who then decided the best way to add to their holdings was to kill their rivals. Gregory of Tours, chief historian of the Merovingian era, said that Clovis, first of the kings, complained loudly that he was alone in the world without any relatives, in the hopes of luring some relatives out of hiding so he could kill them.
The Carolingian kings were not much better (eighth to tenth centuries). Charlemagne had a younger brother, named Carloman, whom Charlemagne's biographer Einhard said died of "some disease." Einhard went on to say that he couldn't imagine why Carloman's widow then fled with her children. (One can imagine just fine.)
Charlemagne's grandsons were each given a kingdom of their own, Germany for Louis, France for Charles, and the "Middle Kingdom" (including Italy) for Lothair. Louis and Charles immediately ganged up on their brother, as perhaps should be expected. In the confusion and disagreements over the next two generations, a kingdom of Burgundy was established within what Lothair had thought was his kingdom, and Boso declared himself king, only to be opposed by his brother Richard, who told the Carolingian kings that he was their little friend.
In England after the 1066 Norman Conquest, William the Conqueror designated Normandy, the family inheritance, for his oldest son, Robert Curthose, designated newly conquered England for his second son, William Rufus, and told Henry, the third son, "Sorry, kid." When William Rufus died without heirs in 1100, Henry immediately took his brother's throne. Robert Curthose was off on Crusade and was understandably shocked when he got home. Extensive fighting then took place, and Henry eventually won, taking Normandy as well as England and locking up his brother for the rest of his life.
In France, it was often remarked in the thirteenth century, with some wonderment, that the younger brothers of the king didn't try to kill him, not even a little. In part this was due to the kings parceling out large chunks of territory (appanages) to their younger brothers.
These examples are all of the most powerful (and there are plenty more examples of fraternal warfare). Peasant families in contrast tended to act in solidarity. After all, they could not call up armies or faithful followers (like Boso's brother Richard) to fight against their relatives. Landlords were more likely than brothers to be seen as the enemy.
© C. Dale Brittain 2023
For more on medieval political and social history, see my ebook Positively Medieval, available on Amazon and other ebook platforms. Also available in paperback.