Irghiz River skirmish

The background events are similar for each possible date: Genghis Khan, khagan of the Mongols, sent an army under his general Subutai to attack hostile forces (either a Merkit confederation or the renegade Naiman prince Kuchlug) in the former lands of the Qara-Khitai dynasty.

Shah Muhammad, the ruler of the Khwarazmian Empire, received news of large armies operating along his northern borders and set out to confront them.

The prowess of the Mongol soldiers displayed during the skirmish has been cited as a major reason for the Shah choosing a defensive strategy during the open warfare of 1220–21, for which this was a preliminary encounter.

[4] Adding to the confusion, all the chronicles contain errors of differing magnitude: for example, Nasawi indicates that the battle came after the defeat of Kuchlug, which is known to have happened no earlier than 1218; by contrast, Juvayni's account states that the Sultan remained in Bukhara from 30 October to 30 December "because it was springtime" — a contradiction in itself.

[9] According to Christopher Atwood, it is certain that both the Shah and the Mongols were campaigning in the drainage area of the Syr Darya in 1209/10, which lends this account credence in geographical terms;[10] it is however supported by fewer sources than the other version.

[11] Other historians suggest that the battle took place in 1218/19, following the accounts set down by al-Athir and Juvayni: this version emphasises the deterioration in relations between Shah Muhammad and Genghis Khan.

It is clear from both Juvayni and Nasawi that the Shah was left momentarily isolated in the centre; however, a cavalry charge from his right wing, possibly led by his son Jalal al-Din, managed to force the enemy back.

The Khwarazmian ruler is reported to have been shaken and even scared by the strength and valour of the Mongol forces; many historians, following Vasily Bartold, cite this reaction as the reason he chose a purely defensive strategy during the invasion.