The Juyan Lake Basin lies along the route of the Northern Silk Road, which is about twenty-six hundred kilometers in length, connecting the ancient Chinese capital of Xian to the west over the Pamir Mountains to emerge in Kashgar before linking to ancient Parthia.

According to C. Michael Hogan, this route greatly expanded in its usage after the Han Dynasty pushed back the northern tribes in the latter part of the first millennium BCE.

Khara-Koto, a city in what is today western Inner Mongolia, near the Juyan Lake, had been founded in 1032 and had become a thriving center of Tangut trade in the eleventh century.

There are remains today of thirty-foot-high ramparts and two-foot-thick outer walls—as much as forty-five yards to a side.

The walled fortress is taken by Genghis Khan in 1225, but—contrary to a widely circulated misunderstanding—the city will continue to flourish under Mongol overlordship.

Genghis now moves to Ganzhou, the hometown of his general Chagaan.

Chagaan's father still commands the city garrison, so Chagaan attempts negotiations with him.

However, the second-in-command of the city stages a coup, kills Chagaan's father, and refuses to surrender.

The city takes five months to subdue, and though the now furious Genghis threatens vengeance, Chagaan convinces him to kill no more than the thirty-five conspirators who had killed Chagaan's father.

Genghis escapes the heat in August 122 by residing in the Qilian Mountains while his troops approach Wuwei, the second-largest city of the Western Xia empire.

As no relief comes from the capital, Wuwei decides to surrender and avoid certain destruction.

At this point, Emperor Xianzong dies, leaving Mozhu to deal with a collapsing state as the Mongols encroach on the capital.

In autumn, Genghis rejoins his troops, takes Liangchow, crosses the Helan Shan desert, and …

…in November lays siege to Lingwu, a mere thirty kilometers from Yinchuan.

Here, in the Battle of Yellow River, Western Xia leads a counterattack with an estimated force of over three hundred thousand troops, engaging Mongol forces along the banks of the frozen river and canal systems.

The Mongols destroy the Western Xia troops, supposedly counting three hundred thousand bodies of Western Xia soldiers after the battle.

Genghis Khan, after defeating Khwarezm in 1221, had prepared his armies to punish Western Xia for their betrayal.

Meanwhile, Emperor Shenzong had stepped down from power in 1223, leaving his second son Lǐ Déwàng, in his place.

As Emperor Xianzong, Lǐ Déwàng reverses his father’s policy and decides to ally with Jin.

However, the Jin Empire is under attack by the Mongol Empire and is unable to help out Western Xia.

When Genghis Khan returns from his campaign, Xianzong pleads with him, but the general Aša-gambu challenges the Mongol ruler.

After taking Khara-Khoto, the Mongols have begun a steady advance southward, attacking with a force of approximately one hundred and eighty thousand.

Aša-gambu, commander of the Western Xia troops, cannot afford to meet the Mongols as it would involve an exhausting westward march from the capital Yinchuan through five hundred kilometers of desert.

Enraged by Western Xia's fierce resistance, Genghis subjects the countryside to annihilative warfare and orders his generals to systematically destroy cities and garrisons as they go.

With no army to meet them in pitched battle, the Mongols pick the best targets for attack and as each city falls the Mongols draw on prisoners, defectors, supplies, and weapons to take the next one.

The Western Xia armies, exhausted by the long and incessant wars against the Jin, are unable to beat back the Mongol assaults.

Two months after taking Khara-Khoto, the Mongols reach a point where the Qilian Mountains force the Etsin River eastward, about three hundred kilometers south of Khara-Khoto.

Here, Genghis divides his army, sending general Subutai to subdue the westernmost cities, while the main force moves east into the heart of the Western Xia Empire.

Genghis lays siege to the Suzhou district, which falls after five weeks.