After 1900, the financial and official records from Henry's reign began to become accessible to historians, including the pipe rolls, court records, correspondence and records of administration of the royal forests. Thomas Tout made extensive use of these new sources in the 1920s, and post-war historians brought a particular focus on the finances of Henry's government, highlighting his fiscal difficulties. This wave of research culminated in Sir Maurice Powicke's two major biographical works on Henry, published in 1948 and 1953, which formed the established history of the King for the next three decades.
By the 19th century, Victorian scholars such as william Stubbs, James Ramsay, and william Hunt sought to understand how the English political system had evolved under Henry. They explored the emergence of Parliamentary institutions during his reign, and sympathized with the concerns of the chroniclers over the role of the Poitevins in England. This focus carried on into early 20th-century research into Henry, such as Kate Norgate's 1913 volume, which continued to make heavy use of the chronicler accounts and focused primarily on constitutional issues, with a distinctive nationalistic bias.
Henry's reign did not receive much attention from historians for many years after the 1950s: no substantial biographies of Henry were written after Powicke's, and the Historian John Beeler observed in the 1970s that the coverage of Henry's reign by military historians remained particularly thin. At the end of the 20th century, there was a renewed interest in 13th-century English history, resulting in the publication of various specialist works on aspects of Henry's reign, including government Finance and the period of Henry's minority. Current historiography notes both Henry's positive and negative qualities: Historian David Carpenter judges Henry to have been a decent man, who failed as a ruler because of his naivety and inability to produce realistic plans for reform, a theme echoed by Huw Ridgeway, who also notes his unworldliness and inability to manage his court, but who considers him to have been "essentially a man of peace, kind and merciful".
The discontent finally erupted in April, when seven of the major English and Savoyard barons – Simon de Montfort, Roger and Hugh Bigod, John Fitzgeoffrey, Peter de Montfort, Peter de Savoy and Richard de Clare – secretly formed an alliance to expel the Lusignans from court, a move probably quietly supported by the Queen. On 30 April, Roger Bigod marched into Westminster in the middle of the King's parliament, backed by his co-conspirators, and carried out a coup d'état. Henry, fearful that he was about to be arrested and imprisoned, agreed to abandon his policy of personal rule and instead govern through a council of 24 barons and churchmen, half chosen by the King and half by the barons. His own nominees to the council drew heavily on the hated Lusignans.
The first histories of Henry's reign emerged in the 16th and 17th centuries, relying primarily on the accounts of medieval chroniclers, in particular writings of Roger of Wendover and Matthew Paris. These early historians, including Archbishop Matthew Parker, were influenced by contemporary concerns about the roles of the Church and state, and examined the changing nature of kingship under Henry, the emergence of English nationalism during the period and what they perceived to be the malign influence of the Papacy. During the English Civil War, historians also drew parallels between Henry's experiences and those of the deposed Charles I.