Mortimer names Plantagenet as his heir, since he has had no children. Plantagenet says his father's death was undeserved, that he was simply the victim of the whims of bloody tyranny, but Mortimer urges him to understand that the house of Lancaster holds the throne firmly by now.
Mortimer tells Plantagenet not to mourn his passing, and he dies. Plantagenet promises to keep Mortimer's advice to himself. But he is determined to right the wrongs Somerset has done to his family, and he hurries off to the Parliament, seeking to gain power in some way, if not restore his inherited rights entirely.
There is no historical fact to suggest that these confrontational scenes in the Temple Garden ever took place, but they symbolize what was an actual break within the English nobility (between the Yorkists and the Lancastrians), which, as Warwick foresees, led to decades of civil unrest, the historical War of the Roses. This disagreement would last until Henry Tudor, a Lancastrian descendant, defeated Richard III, the last of the Yorkist kings, and then married a Yorkist heir, thus, uniting the red and the white rose.
Thus, the play attempts to offer an explanation for the origin of this civil conflict. Yet the reasons Plantagenet and Somerset argue are not laid out with enough clarity for their argument to seem completely warranted. Was one really cheated out of the throne, or do both simply desire the throne for personal and selfish reasons? This scene may serve as an illustration of the origin of these events, but as an actual explanation, it falls somewhat short.
The events described by Mortimer take place in Shakespeare's Richard II. Some historians of Shakespeare's time suggested that by deposing Richard II--the rightful heir--Henry IV committed a crime against God and, thus, incurred punishment in the form of a hundred years of bloody struggle in England. Even Henry V, preparing to attack the French in Henry V, worries he will be punished for the crimes of his father. The later events depicted in Richard III, when a truly merciless king succeeds Henry VI, illustrate the heights of depravity reached by a family line that may not have rightfully held the throne in the first place. All this was finally repaired by Henry VII when the red and the white rose became one again via his marriage. Shakespeare, writing in the time of the rule of Queen Elizabeth, the last of the York line, took pains to suggest that the York family was the rightful heir to the throne and that the unfortunate struggle of the War of the Roses led to the rightful--indeed, divine--installation of Elizabeth's forefathers on the throne. Hence Shakespeare's history of the dispute is never impartial, often subtly privileging the York side.