The usurper Wang Mang sends his ambassadors to the Xiongnu in 10 to inform Chanyu Zhi that he has become emperor and that Xin has replaced Han, and requests that the great seal of the chanyu, which the Han had issued, be exchanged for a new seal issued by Xin.

The old seal reads, "the Great Seal of the Chanyu of Xiongnu", while the new seal reads, "the Seal of the Shanyu of Gongnu of Xin", changing the meanings "ferocious vassal" to "respectful vassal", "Chanyu" to "Shanyu", and "seal" to "badge", implying that the Xiongnu polity, which the Han had treated with some ambiguity about whether it was a vassal, is clearly a vassal of Xin.

Without examining the new seal, Chanyu Zhi agrees to the exchange.

The ambassadors, apprehensive that the Chanyu, once he realizes what had happened, would demand the old seal back, destroy the old seal.

Indeed, the next day, the Chanyu realizes that the seal text had changed, and requests that the old seal be returned, but upon being informed that the old seal had been destroyed (which the ambassadors claimed falsely to be an act of the gods), acquiesces.

Chanyu Zhi, however, begins to prepare for confrontation with the Xin dynasty.

He builds defensive bulwarks some distance from the Xin outpost of Shuofang (roughly modern Ordos, Inner Mongolia).

He also begins to accept the Xiyu ("Western Yu", in modern Xinjiang and former Soviet central Asia) kingdoms' pledges of allegiance, which were banned previously by Wang.

Wang, irritated with Chanyu Zhi, declares war against Xiongnu.

The strategy that he sets out is to divide the Xin forces into twelve armies to divide and conquer Xiongnu.

Under this scenario, Chanyu Zhi would be attacked and forced to retreat to the Dingling tribes (around Lake Baikal), and Xiongnu would be divided into fifteen small kingdoms to be ruled by fifteen descendants of Chanyu Huhanye, who had first established friendly relations with Han.

Under this plan, three hundred thousand men would be gathered (and would attack at the same time).

Wang does not follow his generals' recommendations to start the campaign as soon as a critical mass of men is gathered, but wants to attack with overwhelming force.

This causes the border regions to become strained with accommodating the men who had already arrived for years, while fruitlessly waiting for the full support of three hundred thousand to be gathered.

One of the local commanders kidnaps one of Chanyu Zhi's brothers, Xian, the Prince of Zuoliwu, and his sons Deng and Zhu, by trickery in the first stage of Wang Mang’s plan.

Xian and Zhu are made Chanyus—to be two of the fifteen.

An enraged Chanyu Zhi initiates massive attacks against Xin border regions, causing the border regions much distress and loss in economic and human terms.

Eventually, Xian escapes back to Xiongnu, but his sons are kept as hostages.

After Zhu dies, Deng succeeds him.

However, in 12, after hearing reports that Xian's other son Jiao had been a successful Xiongnu strategist in military actions, Wang, in anger, executes Deng and his attendants.

Chanyu Zhi dies later in 13, and the powerful official Xubu Dang and his wife Yun, the Princess Yimuo (the daughter of Chanyu Huhanye and Wang Zhaojun), who advocates peaceful relations with the Xin dynasty and who are also friendly with Xian, support Xian as the new Chanyu, but even though Xian is unaware that Wang Mang had executed his son Deng, their friendly relations do not return.

There is a temporary détente in 14, when Xian returns Xin defectors Chen Liang and Zhong Dai who, as junior army officers in Xiyu, had killed their superiors and surrendered to the Xiongnu (perhaps seeking to have the Xiongnu help them reestablish Han rule) so that Wang could execute them.

In reciprocation, Wang recalls the forces to the northern regions that had been intended to attack Xiongnu (but have never received the full support that Wang had envisioned).

However, after Chanyu Xian discovers, late in 14, that Deng had been executed, he resumes raids against the border regions but maintains a façade of peaceful intention.

Lu Fang, who also claims the name Liu Wenbo and claims to be a descendant of Emperor Wu and the proper Han emperor, is supported by Xiongnu's Chanyu Yu; he controls the modern central and western Inner Mongolia region.

Some Russian archaeologists have identified a Han-era Chinese-style palace unearthed near Abakan (in Southern Siberia) in 1941-45 as Lu Fang's residence after he had left China for the lands of the Xiongnu.

China is by this point completely unified by the Tang dynasty except for the domain of Liang Shidu the Emperor of Liang, who controls modern northern Shaanxi and western Inner Mongolia, although, with Li Fuwei at Chang'an, Fu Gongshi rebels in 623 and declares himself the Emperor of Song.

Fu's rebellion, however, will be quelled by Li Xiaogong in 624.