|Ab urbe condita||1987|
|Balinese saka calendar||1155–1156|
|English Regnal year||18 Hen. 3 – 19 Hen. 3|
|Chinese calendar||癸巳年 (Water Snake)|
3930 or 3870
— to —
甲午年 (Wood Horse)
3931 or 3871
|- Vikram Samvat||1290–1291|
|- Shaka Samvat||1155–1156|
|- Kali Yuga||4334–4335|
|Japanese calendar||Tenpuku 2 / Bunryaku 1|
|Minguo calendar||678 before ROC|
|Thai solar calendar||1776–1777|
1360 or 979 or 207
— to —
1361 or 980 or 208
|Wikimedia Commons has media related to 1234.|
- The Manden region rises against the Kaniaga Kingdom. This is the beginning of a process that will lead to the rise of the Mali Empire.
- February 9 – Mongol conquest of the Jin dynasty: In the Siege of Caizhou, Song Dynasty Chinese and Mongolian armies occupy the Jurchen capital at Caizhou, and Emperor Aizong of Jin commits suicide, marking the collapse of the Jin Dynasty.
- Upon the death of Knut Långe, the deposed Erik Eriksson returns as king of Sweden, possibly after a small war between the two of them. It is also possible that Knut dies of natural causes, and Erik peacefully then returns as king.
- Pope Gregory IX calls for a crusade against Bosnia, and replaces the Bogumil Bosnian Bishop with a Catholic Dominican German, Johann.
- King Andrew II of Hungary proclaims herzeg Coloman as Ban of Bosnia, who passes it on to Prijezda, a cousin of Ban Matej Ninoslav (1234 to 1239), despite Matej being the legitimate Ban of Bosnia.
- Sancho II of Portugal conquers the cities of Aljustrel and Mértola from the Muslims.
- Saint Dominic is canonized.
- Pope Gregory IX releases the Nova Compilatio Decretalium or Decretales Gregorii IX.
- April 16 – Richard Marshal, 3rd Earl of Pembroke (b. 1191)
- May 7 – Otto I, Duke of Merania (b. c. 1180)
- June 18 – Emperor Chūkyō of Japan (b. 1218)
- August 7 – Hugh Foliot, bishop of Hereford (b.c. 1155)
- August 31 – Emperor Go-Horikawa of Japan (b. 1212)
- December – Inga of Varteig, Norwegian royal mistress (b. c. 1185)
- date unknown