The tensions between Yi Bangwon's faction and Yi Banggan's camp escalate in 1400 into an all-out conflict that will come to be known as the Second Strife of Princes.

In the aftermath of the struggle, the defeated Yi Banggan is exiled to Tosan, while those who had urged him to battle against Yi Bangwon are executed.

Thoroughly intimidated, King Jeongjong immediately invests Yi Bangwon as heir presumptive and voluntarily abdicates.

This same year, Yi Bangwon finally assumes the throne of Joseon as King Taejong.

A well-preserved mammoth, frozen many thousands of years before, is found in Siberia in 1400.

Smolensk under its hereditary ruler, Yury of Smolensk, and his father-in-law, Oleg Korotopol of Ryazan, revolts from Lithuania, not long after the Lithuanian defeat at the Battle of the Voskla River, battle; the pro-Lithuanian boyars in Bryansk and ...

… Smolensk are promptly executed.

In the fall, Vytautas lays siege to Smolensk but is forced to retreat after signing an armistice.

Vytautas' total defeat at the Vorskla comes as a shock to the Grand Duchy of Lithuania and Poland, effectively blocking Lithuanian expansion to Southern Ruthenia, ending Vytautas' imperial ambitions in the east, and obliging him to submit once more to the protection of Wladyslaw.

His enormous state has also lost hard-won access to the Black Sea, as the Tatars have reconquered the southern steppe all the way to Moldavia; land that will not be reclaimed untils ome forty-two years later when the Crimean Khanate breaks away from the Golden Horde.

The “Elbing Vocabulary,” a short German-Prussian glossary written between 1300 and 1400, provides one of the few written documentations of Prussian, the West Baltic language sometimes called Old Prussian.

The most conservative of all Baltic languages, the Prussian of the Elbing vocabulary contains more archaisms than Lithuanian and differs significantly from both Lithuanian and Lettish, or Latvian.

Spoken by the inhabitants of the area that later became East Prussia (now northeastern Poland and the Kaliningrad Oblast of Russia) prior to the German colonization of the area which began in the thirteenth century, it will become extinct in the seventeenth century.

A few experimental communities involved in reviving a reconstructed form of the language exist today in Lithuania, Poland, and other countries.

Mircea defeats yet another expedition of Turks crossing the country in 1400 and extends his rule to the Danube Delta, Dobruja, and Silistra, transferring his capital from Curtea Agues to Tirgoviste.

Sultan Ahmad, fearing that he will be attacked when Timur returns from campaigns in the east in 1400, leaves Baghdad; he returns for a short while but then leaves again, taking refuge with the Ottomans.

Qara Yusuf, like Sultan Ahmad Jelair, flees from Timur and takes refuge with the Ottoman Sultan.

Timur, exasperated by the Ottoman maneuvers, seizes Sivas in August 1400; …