At first the
Khalkha and Oirat Mongols were allies, bound by the provisions of the Mongol-Oirat code. To cement this union, Galdan attempted to ally with
Zasaghtu Khan Shira who lost part of his subjects to
Tushiyetu Khan Chakhun Dorji, and moved his
orda near the
Altai Mountains.
Tushiyetu Khan attacked the right wing of the Khalkhas and killed Shira in 1687. Galdan dispatched troops under his younger brother
Dorji-jav against the
Tushiyetu Khan the next year, but they were eventually defeated and Dorji-jav was killed in the ensuing battle. Chakhundorji murdered Degdeehei Mergen Ahai of the Zasaghtu Khan who was on the way to Galdan. The
Qing court intervened and called all the Mongolian nobles to assemble a conference. To avenge the death of his brother and expand his influence over other Mongol areas, Galdan prepared for war with the Khalkha of eastern Mongolia. Galdan established a friendly relationship with the
Tsardom of Russia, which was at war with Tushiyetu Khan over territories near
Lake Baikal in northern Khalkha. Bonded by a common interest in defeating the Khalkha, both Galdan and the Russians simultaneously attacked and conquered most of the territories of Khalkha. Armed with superior firearms provided by the Russians, Galdan attacked the land of the late
Zasaghtu Khan, and advanced to the dominion of Tushiyetu Khan. The
Russian Cossacks meanwhile attacked and defeated the Khalkha's contingent of 10,000 near
Lake Baikal.. In 1688, after two bloody battles with the Dzungar in present-day central Mongolia,
Erdene Zuu Monastery and Tomor, Tushiyetu Khan and his son Galdandorji fled to the
Ongi River. Acting in defiance of contrary orders from the
Kangxi Emperor and the
5th Dalai Lama, he entered Khalkha territory in 1688. The Zunghars occupied the Khalkha homeland, and forced
Jibzundamba Zanabazar to flee. The Qing court strengthened its northern border garrisons, and advised the Khalkhas to resist Galdan. After being reinforced by fresh troops, the Tushiyetu Khan Chakhundorji counterattacked the Zunghars, and fought with them near Olgoi Lake on August 3, 1688. The Oirats won after a 3-day battle. Galdan's conquest of Khalkha Mongolia made Zanabazar and Chakhundorji submit to the
Qing dynasty in September. == War with the Qing ==