List of heads of state 840

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Africa

• Aghlabids
  • Emir : al-Aghlab ibn Ibrahim I (838-841)
• Idrisids in Morocco
  • Imam : Ali I. Haydara ibn Muhammad (836-849)
• Rustamids
  • Imam : Aflah ibn 'Abd al-Wahhab (824-872)

Asia

• Bagan
  • King : Hkelu (829–846)

• China
  • Emperor : Tang Wenzong (826-840)
  • Emperor: Tang Wuzong (840–846)

• India
  • Eastern Chalukya
    • King : Vijayaditya II (808–847)
  • Pala
    • King : Devapala (810–850)
  • Pallava
    • King : Nandi Varman III. (825-850)
  • Pandya
    • King : Sirmara Srivallabha (830–862)
  • Pratihara
    • King : Samrat Mihir Bhoja Mahan (836-885)
  • Rashtrakuta
    • King : Amoghavarsha I (814–878)

• Japan
  • Emperor : Nimmyō (833-850)

• Khmer
  • King : Jayavarman II (802-850)

• Korea
  • Balhae
    • King : Jangjong Hwa (832–858)
  • Silla
    • King : Munseong (839-857)

• Caliphate of the Muslims
  • Caliph : al-Mu'tasim bi-'llāh (833-842)

• Nanzhao
  • King : Meng Quanfengyou (823–859)

• Tao-Klardschetien
  • Kuropalat : Bagrat I. (830–876)

• Tibet
  • King : Lang Darma (836–842)

Europe

• Bulgaria
  • Khan : Presian I. (836-852)

• Byzantine Empire
  • Emperor : Theophilos (829-842)

• England ( heptarchy )
  • East Anglia
    • King : Æthelstan (827–845)
  • Essex
    • King : Sigeric II. (825–840)
  • Mercia
    • King : Wiglaf (830-840)
    • King: Beorhtwulf (840–852)
  • Northumbria
    • King : Eanred (810-840)
    • King: Æthelred II (840–844)
  • Wessex
    • King : Æthelwulf (839–855)

• Frankish Empire
  • King: Louis the Pious (814–840)
  • Fraternal war and division of the empire (cf. inner dynastic battles of the Carolingians 830–842 ) (840–843)
  • West Franconia
    • Maine
      • Count : Gauzbert I. (839–849)
    • Toulouse county
      • Count : Bernhard of Septimania (835–844)
  • Eastern Franconia
    • Saxony
      • Duke : Liudolf (approx. 840–866)

• Italy
  • Papal States
    • Pope : Gregory IV (827-844)
  • Naples
    • Duke : Sergius I (840–864 / 865)
  • Salerno
    • Prince : Siconulf (840–851)
  • Venice
    • Doge of Venice : Pietro Tradonico (836–864)

• Moravian Empire
  • Prince: Mojmir I. (833–846)

• Raszien
  • Großžupan : Vlastimir (825–860)

• Scotland
  • Dalriada
    • King : Alpin II. (839–841)
  • Strathclyde
    • King : Dumnuagal IV. (Approx. 810 – approx. 840)
    • King: Artgal (approx. 840–872)
  • Picts
    • King : Uen (839–842)

• Spain
  • Asturias
    • King : Alfonso II (791–842)
  • Barcelona county
    • Count : Bernhard of Septimania (835–844)
  • Emirate of Cordoba
    • Emir: Abd ar-Rahman II (822-852)
  • Navarre
    • King : Íñigo Arista (824–852)

• Wales
  • Gwynedd
    • Prince : Merfyn Frych (825–844)
  • Powys
    • Prince: Cyngen ap Cadell (808–854)