Stafford returned to the French campaign during the 1430s and for his loyalty and years of service, he was elevated from Earl of Stafford to Duke of Buckingham. Around the same time, his mother died. As much of his estate—as her dower—had previously been in her hands, Humphrey went from having a reduced income in his early years to being one of the wealthiest and most powerful landowners in England. His lands stretched across much of the country, ranging from East Anglia to the Welsh border. Being such an important figure in the localities was not without its dangers and for some time he feuded violently with Sir Thomas Malory in the Midlands.
After returning from France, Stafford remained in England for the rest of his life, serving King Henry. He acted as the King's bodyguard and chief negotiator during Jack Cade's rebellion of 1450, helping to suppress it. When the King's cousin, Richard, Duke of York, rebelled two years later, Stafford investigated York's followers. In 1453, the King became ill and sank into a catatonic state; law and order broke down further and when civil war began in 1455, Stafford fought for the King in the First Battle of St Albans which began the Wars of the Roses. Both were captured by the Yorkists and Stafford spent most of his final years attempting to mediate between the Yorkist and Lancastrian factions, the latter by now headed by Henry's wife, Margaret of Anjou. Partly due to a feud with a leading Yorkist—Richard Neville, Earl of Warwick—Stafford eventually declared for King Henry and the Duke of York was defeated in 1459, driving York into exile. When the rebels returned the following year they attacked the royal army at Northampton. Acting as the King's personal guard in the ensuing struggle, Stafford was killed and the King was again taken prisoner. Stafford's eldest son had died of plague two years earlier and the Buckingham dukedom descended to Stafford's five-year-old grandson, Henry, a ward of the King until he came of age in 1473.
On 21 July 1403, when Humphrey was less than a year old, his father was killed fighting for Henry IV against the rebel Henry Hotspur at the Battle of Shrewsbury. Humphrey became 6th Earl of Stafford. With the earldom came a large estate with land in more than a dozen counties. Through her previous marriage to Edmund's older brother, Thomas, she accumulated two dowries,[note 1] each comprising a third of the Stafford estates. She occupied these lands for the next twenty years, and Humphrey received a reduced income of less than £1,260 a year until he came of age. As his mother could not, by law, be his guardian, Humphrey became a royal ward and was put under the guardianship of Henry IV's queen, Joan of Navarre. His minority lasted for the next twenty years.