Edmund Beaufort, second Duke of Somerset, was more a formidable player than his brother - not that that took much - but as indicated in the last post was handicapped by relative poverty, so much of the family's livelihood having passed to his niece, Margaret Beaufort. This in turn made it essential for him to have power at court in order to secure offices and anything else that turned up in the way of patronage. Fortunately for him, he seems to have had no difficulty winning and retaining the favour of King Henry VI and Queen Margaret of Anjou.
Early in his life Edmund had an association - perhaps even an affair - with Katherine of Valois, Henry V's widow in 1426-7, and it seems to have been this that caused the Council to impose formal restrictions on Katherine's right to re-marry. However - it is only fair to point this out in view of Yorkist criticism of Somerset's later record - in the 1430s Edmund became one of England's more successful generals in the French wars. He successfully defended Calais in 1436 and in 1439-40 was responsible for the very last English successes of the war, the relief of Avranches and recapture of Harfleur. On the other hand, even in the mid 1430s he came under criticism for misconduct, particularly for putting his own personal interests above those of the English cause.
Edmund married Eleanor Beauchamp, daughter of Richard Beauchamp Earl of Warwick by his first wife, Elizabeth Berkeley, and widow of Lord Roos of Hamlake. This match was destined to lead him into a serious quarrel with the Nevilles, and was one of the root causes of the Wars of the Roses.
When Richard Beauchamp died, his lands (apart from the Berkeley element, of which more later) passed to his son, Henry, later (and briefly) Duke of Warwick. (Henry was a child of Beauchamp's second marriage, to Isabelle Despenser.) When Henry died a few years later he left behind a daughter, Anne (by Cecille Neville) but unfortunately this child also died in infancy.
This meant that the Beauchamp inheritance had to be split between Richard Beauchamp's four daughters.
There were three elements of the inheritance:
1. Elizabeth Berkeley's Berkeley inheritance, disputed by her cousin, Lord Berkeley, and split three ways between her daughters.
2. The Beauchamp inheritance proper, coming from Richard Beauchamp.
3. The Despenser/Burghersh inheritance, coming from Isabelle Despenser and clearly divisible between the two daughters of Isabelle by her two husbands. This included Glamorgan.
However - it was held that because Anne Beauchamp, the Kingmaker's wife, was whole-blood heir to Henry, Duke of Warwick, she should have the whole of element '2' to the exclusion of her half-sisters. They, and their husbands, were distinctly unchuffed by this. John Talbot, Earl of Shrewsbury, for example, felt that as he was married to the eldest sister he ought to be Earl of Warwick!
As if this was not complicated enough, Richard Beauchamp and his son had kept hold of most of the inheritance (including all Glamorgan) that ought to have been shared with Elizabeth Beauchamp, the elder daughter of Isabelle Despenser. Richard Neville, as Earl of Warwick, continued to retain these lands.
It's not really clear to me why Somerset felt that he was entitled to half of Glamorgan, but for some reason he did, and this led to a violent dispute with the Kingmaker. This was undoubtedly one of the factors that turned Warwick (and his father Salisbury) from Lancastrian supporters into committed Yorkists. Henry VI seems to have been totally incapable of settling this kind of dispute, a factor that helped bring about his downfall. (Contrast how the supposedly ineffective Richard II settled the dispute between the Beauchamps and Mowbrays over Gower, with a fairly harsh decision that nevertheless was not overturned by the usurping Henry IV.)
I think that's enough to digest for one day. So Edmund will get a second posting in a little time.