Why did Richard, duke of York, have a strong claim to the English throne?

Richard, 3rd Duke of York, held a strong hereditary claim to the English throne based on the principles of primogeniture and lineal descent from Edward III.12

His claim was rooted in two primary lines of descent:
* Maternal Line: Through his mother, he was a descendant of Lionel of Antwerp, Duke of Clarence, the second surviving son of Edward III.23
* Paternal Line: Through his father, he was a descendant of Edmund of Langley, 1st Duke of York, the fourth surviving son of Edward III.3

Because the House of Lancaster descended from John of Gaunt—a younger brother of Lionel of Clarence—Richard’s supporters argued that his hereditary right was superior to that of the reigning monarch, Henry VI. While some contemporaries, such as Chief Justice John Fortescue, objected that the claim was derived through females, Richard’s position was bolstered by his descent from the Mortimer family, who had been considered the rightful heirs to Richard II.234