List of state leaders in 840

Asia

• Bohai/Balhae - Da Yizhen/Dae I-jin , King of Bohai/Balhae (830-857)
• China (Tang Dynasty) -
  1. Wenzong , Emperor of Tang China (826-840)
  2. Wuzong, Emperor of Tang China (840-846)
• Gurjara - Mihira Bhoja I , Pratihara King of Gurjara (c. 836-886)
• Japan (Heian Period) - Nimmyo, Emperor of Japan (833-850)
• Silla - Munseong , King of Silla (839-857)

Europe

• Dalriada - Alpin II, King of Dalriada (839–842)
• East Anglia¹ - Æthelweard , King of East Anglia (839–855)
• England - Æthelwulf of Wessex, Bretwalda (839–856)
• Mercia -
  1. Wiglaf, King of Mercia (830–840)
  2. Wigstan, King of Mercia (840–840)
  3. Beorhtwulf, King of Mercia (840–852)
• Northumbria¹ - Eanred, King of Northumbria (810–841)
• Ireland -
  • Nial Caille , High King of Ireland (832–844)
  • Turgesius of Norway , High King of Ireland (832–845)
• Picts - Uurad , King of the Picts (839–842)
• Strathclyde - Arthgal f Dyfnwal , King of Strathclyde (816–872)
• Wales - Merfyn Frych ap Gwriad , King of Gwynedd (825–844)

Notes

1. Though East Anglia, Northumbria and Mercia are traditionally perceived to have been in the heptarchy they were largely independent kingdoms until its conquest by the Danes in 869 and 867, respectively - where Mercia was conquered by Wessex in 874. All other members of the heptarchy had been conquered by Wessex and by this time had no form or king.