In what ways could a cadet branch come into life? Why would a younger sibling in a royal or noble house start his own as a cadet branch?
This information is for personal, non-historical, writing; therefore the most useful answers would be ones that simply give me the reasons why it would happen in general. For instance, the specific political reasonings behind the making of a cadet branch in a single house I fear would simply go over my head. I would like the general reasons why it could happen that could apply to any royal or noble house, real or otherwise.