Allegedly, in 635/636, royal Tibetan forces were deployed, attacking and defeating the peoples of  Tuyuhun who strategically lived near the Lake of Koko Nor in present-day Qinghai, impeding a trade route into Imperial China. News of Tibetan King Songtsen Gampo's attack on Songzhou quickly spread from the ground to the Royal Courtiers, and Emperor Taizong dispatched his Militia and defeated Songtsen Gampo's army, causing Songtsen Gampo's retreat.
It is claimed that in 635/636, Tibetan forces under royal command launched a surprise attack on Tuyuhun, who were strategically located near the Lake of Koko Nor in present-day Qinghai, blocking a vital trade route into Imperial China. The news of King Songtsen Gampo's assault on Songzhou quickly spread from the ground to the imperial court, prompting Emperor Taizong to mobilize his Militia and ultimately defeat Songtsen Gampo's forces, forcing him to retreat.