In medieval England, the crown passed from the father to the first-born son, then to the second-born son, and so on. But the younger sons could not inherit until the line of the older son was extinct. (So a first-born grandson was ahead of a second-born son in the line of succession.) Thus Mortimer, a descendant of Edward III’s second-born son Lionel of Antwerp, has a stronger claim to the crown than King Henry IV, the son of Edward III’s third-born son: John of Gaunt.
Henry Bolingbroke accuses Thomas Mobray of treason. Bolingbroke and Mobray agree to settle their dispute in a duel. But King Richard II stops them at the last moment, declares them both guilty, and banishes them—Bolingbroke for six years, Mobray for life.
When Bolingbroke’s father (John of Gaunt) dies, Richard II sizes his estate to finance a war against Ireland. Richard II’s actions trouble Northumberland, who fears this precedent will allow the King to seize any nobleman’s lands and money.
With Northumberland’s help, Bolingbroke returns to England not only to regain his rightful inheritance but to seize the throne as well. Bolingbroke deposes Richard II and has him imprisoned. Henry Bolingbroke is then crowned King Henry IV.
A follower of Bolingbroke’s murders Richard in prison, hoping to curry the new King’s favor. Though not directly responsible for Richard’s death, Henry IV feels guilty and plans a pilgrimage to the Holy Land as penance.
1 Henry IV – Background & Genealogy