Year 1400 (MCD) was a leap year starting on Thursday of the Julian calendar. The year 1400 wasn't a leap year in the Proleptic Gregorian calendar.
|Ab urbe condita||2153|
|Balinese saka calendar||1321–1322|
|English Regnal year||1 Hen. 4 – 2 Hen. 4|
|Chinese calendar||己卯年 (Earth Rabbit)
4096 or 4036 — to — 庚辰年 (Metal Dragon) 4097 or 4037
|- Vikram Samvat||1456–1457|
|- Shaka Samvat||1321–1322|
|- Kali Yuga||4500–4501|
|Japanese calendar||Ōei 7
|Minguo calendar||512 before ROC
|Thai solar calendar||1942–1943|
(female Earth-Rabbit) 1526 or 1145 or 373 — to — 阳金龙年 (male Iron-Dragon) 1527 or 1146 or 374
- January – Henry IV of England stops the Epiphany Rising and kills the Earls of Kent, Huntingdon and Salisbury and the Baron le Despencer, because they tried to have Richard II made as king.
- February – Henry Percy (Hotspur) leads English army into Scotland.
- February 14 – Richard II of England dies in Pontefract Castle but we don't know what killed him. King Henry IV might have ordered people to starve him to death.
- March 23 – Five-year-old Trần Thiếu Đế is forced to stop being the ruler of Đại Việt (modern-day Vietnam) and give the throne to his maternal grandfather Hồ Quý Ly. This was the end of the Trần Dynasty after 175 years and the start of the Hồ Dynasty. Hồ Quý Ly changes the country's name to Đại Ngu.
- May – Frederick I, Duke of Brunswick-Lüneburg tries to take over from Wenceslaus, King of the Romans. However, Frederick is murdered shortly after.
- August 21 – Rupert, Count Palatine of the Rhine, is elected as King of the Romans.
- September 16 – Owain Glyndŵr is made Prince of Wales by the Welsh, and he starts attacking English castles in north-east Wales.
- November – Sack of Aleppo (1400) during Timur's conquest of Syria.
- December – Manuel II Palaiologos becomes the only Byzantine Emperor ever to visit England.
- Timur wins against the Ottoman Empire and the Mamluk Sultanate of Egypt. Timur captures the city of Damascus what is today Syria. Timur's army kills many of the city's people.
- Timur conquers the Empire of the Black Sheep Turkomans, in present-day Azerbaijan, and the Jalayirid Dynasty in present-day Iraq. Black Sheep ruler Qara Yusuf and Jalayirid Sultan Ahmad run away and go to live with the Ottoman Sultan Bayezid I.
- In modern-day Korea, King Jeongjong of Joseon stops being king because he is afraid his younger brother, Taejong, will attack him. Taejong becomes king.
- Prince Parameswara starts the Malacca Sultanate, in what is western Malaysia and northern Sumatra today.
- Hananchi succeeds Min as King of Hokuzan in what is Okinawa, Japan today.
- Wallachia (modern-day southern Romania) stops the Ottomans from invading.
- A Wallachian army captures Iuga, and makes Alexandru cel Bun the Prince of Moldavia.
- The Kingdom of Kongo begins.
- The Haast's eagle and Moa are both made extinct by Māori hunters.
- The Mississippian culture starts to decline.
- Europe is reported to have around 52 million inhabitants.
- The House of Medici becomes powerful in Florence.
- Newcastle upon Tyne is created a county corporate by Henry IV of England.
- Jean Froissart completes his Chronicles, detailing the events of the 14th Century in France.
- January 13 – Infante John of Portugal, the Constable (d. 1442)
- May 19 – John Stourton, 1st Baron Stourton, English baron (d. 1462)
- July 26 – Isabel le Despenser, Countess of Worcester, English noble (d. 1439)
- December 25 – John Sutton, 1st Baron Dudley, Lord Lieutenant of Ireland (d. 1487)
- date unknown
- James Tuchet, 5th Baron Audley (d. 1459)
- Luca della Robbia, Florentine sculptor (d. 1482)
- Isabella, Duchess of Lorraine (d. 1453).
- Richard Neville, 5th Earl of Salisbury, English politician (d. 1460)
- Owen Tudor, Welsh courtier (d. 1461)
- Rogier van der Weyden, Dutch painter (or 1399)
- Hans Multscher, German painter and sculptor (d. 1467)
- Helene Kottanner, Hungarian writer and courtier (d. after 1470)
- probable – Marina Nani, Venetian dogaressa (d. 1473)
- probable – Giovanna Dandolo, Venetian dogaressa (d. after 1462)
Richard II of England
- January 7
- Thomas Holland, 1st Duke of Surrey, English politician (executed) (b. 1374)
- John Montagu, 3rd Earl of Salisbury, English earl (executed) (b. 1350)
- January 13 – Thomas le Despenser, 1st Earl of Gloucester, English politician (executed) (b. 1373)
- January 16 – John Holland, 1st Duke of Exeter, English politician (executed)
- February 14 – King Richard II of England, (probably murdered) (b. 1367)
- April 21 – John Wittlebury, English politician (b. 1333)
- April 23 – Aubrey de Vere, 10th Earl of Oxford, third son of John de Vere (b. 1338)
- April 28 – Baldus de Ubaldis, Italian jurist (b. 1327)
- June 5 – Frederick I, Duke of Brunswick-Lüneburg, rival King of the Romans
- June 17 – Jan of Jenštejn, Archbishop of Prague (b. 1348)
- October 25 – Geoffrey Chaucer, English poet (b. c. 1343)
- November 8 – Peter of Aragon, Aragonese infante (b. 1398)
- November 20 – Elizabeth of Moravia, Margravine of Meissen (b. 1355)
- November – Tarabya of Ava (b. 1368)
- December – Archibald the Grim, Scottish magnate (b. 1328)
- date unknown – Narayana Pandit, Indian mathematician (b. 1340)