structural:expansion, linguistic:paraphrasing
Pre-regnal history

Richard II made his uncle (Edward III's fourth son) Edmund the first duke of York in 1385. Edmund was married to Isabella, a daughter of King Peter of Castile and María de Padilla and the sister of Constance of Castile, who was the second wife of Edmund's brother John of Gaunt. Both of Edmund's sons were killed in 1415. The younger, Richard, became involved in the Southampton Plot, a conspiracy to depose Henry V in favour of Richard's brother-in-law Edmund Mortimer. When Mortimer revealed the plot to the king, Richard was executed for treason. Richard's childless older brother Edward was killed at the Battle of Agincourt later the same year.

Constance of York was Edmund's only daughter and was an ancestor of Queen Anne Neville. The increasingly interwoven Plantagenet relationships were demonstrated by Edmund's second marriage to Joan Holland. Her sister Alianore Holland was mother to Richard's wife, Anne Mortimer. Margaret Holland, another of Joan's sisters, married John of Gaunt's son. She later married Thomas of Lancaster, John of Gaunt's grandson by King Henry IV. A third sister, Eleanor Holland, was mother-in-law to Richard Neville, 5th Earl of Salisbury — John's grandson by his daughter Joan Beaufort, Countess of Westmorland. These sisters were all granddaughters of Joan of Kent, the mother of Richard II, and therefore Plantagenet descendants of Edward I.

Edmund's son Richard was married to Anne Mortimer, the daughter of Roger Mortimer, 4th Earl of March and Eleanor Holland and great-granddaughter of Edward III's second surviving son Lionel. Anne died giving birth to their only son in September 1411. Richard's execution four years later left two orphans: Isabel, who married into the Bourchier family, and a son who was also called Richard.

Although his earldom was forfeited, Richard (the father) was not attainted, and the four-year-old orphan Richard was his heir. Within months of his father's death, Richard's childless uncle, Edward Duke of York, was killed at Agincourt. Richard was allowed to inherit the title of Duke of York in 1426. In 1432 he acquired the earldoms of March and Ulster on the death of his maternal uncle Edmund Mortimer, Earl of March, who had died campaigning with Henry V in France, and the earldom of Cambridge which had belonged to his father.

Being descended from Edward III in both the maternal and the paternal line gave Richard a significant claim to the throne if the Lancastrian line should fail, and by cognatic primogeniture arguably a superior claim. He emphasised the point by being the first to assume the Plantagenet surname in 1448. Having inherited the March and Ulster titles, he became the wealthiest and most powerful noble in England, second only to the king himself. Richard married Cecily Neville, a granddaughter of John of Gaunt, and had thirteen or possibly fifteen children: