After the establishment of the Han Dynasty, Liu Bang began managing various state affairs and discovered a troubling issue. On the northern grasslands and deserts lived a large number of ethnic minorities, whom the Han people called the Xiongnu. After unifying the realm, Qin Shi Huang had sent the great general Meng Tian to fight the Xiongnu, recovering the Hetao region. As the Qin Dynasty declined, the Xiongnu leader Touman Chanyu was killed by his own son, Modu Chanyu. After taking power, Modu annexed other small tribal regimes, growing increasingly powerful. Taking advantage of the Chu-Han conflict, he recaptured the Hetao region and also occupied Zhaona (present-day southeast of Guyuan, Ningxia Hui Autonomous Region) and Fushi (present-day south of Yulin, Shaanxi Province), casting a covetous eye on the Central Plains.
After the Han Dynasty was established, King Xin of Han was granted the title of king by Liu Bang for his outstanding military achievements, receiving the Yingchuan region with its capital at Yangdi.
In 201 BCE, Emperor Gaozu of Han, Liu Bang, grew concerned that the Kingdom of Han, ruled by King Xin of Han, was located too close to the northern nomadic tribes and might collude with the Xiongnu in the future. Using the pretext of defending against Xiongnu invasions, Liu Bang ordered King Xin to relocate from Yangdi (present-day Yuzhou, Henan) to Jinyang (present-day Taiyuan, Shanxi). However, King Xin requested permission to move to Mayi (present-day Shuozhou, Shanxi) instead, and Liu Bang agreed. Shortly after King Xin settled in Mayi, the Xiongnu launched an attack on the city. This deepened Liu Bang's suspicions, and he sent a harshly worded letter to King Xin. Realizing that Liu Bang had already misunderstood him, King Xin decided to go all the way and indeed allied with Modu Chanyu to attack the Han dynasty together, voluntarily offering Mayi to Modu. Subsequently, King Xin led Xiongnu forces to breach the Yanmen Pass and marched southward, capturing the Taiyuan Commandery.
In 200 BCE, Emperor Gaozu of Han, Liu Bang, decided to personally lead an expedition to subdue the Xiongnu and suppress King Xin of Han. Initially, the Han forces achieved consecutive victories; during the battle at Tongdi (near present-day Qin County, Shaanxi), King Xin's army suffered heavy losses, with one of his generals killed by Han troops. King Xin repeatedly fled in defeat and eventually sought refuge among the Xiongnu. Several of his subordinates then found Zhao Li, a descendant of the royal family of the Warring States period's Zhao state, installed him as king, and regrouped the remnants of King Xin's forces to continue fighting against the Han army.
The Xiongnu set up an extensive defensive line stretching from Guangwu (present-day Yangmingbao Town, Daizhou, Shanxi) to Jinyang, aiming to block the Han army's northward advance. The Han forces broke through this line, and the battle at Jinyang inflicted heavy losses on both Han Xin, the King of Han, and the Xiongnu troops. Later, the Han army defeated them a third time at Lishi (present-day Lishi District, Lüliang, Shanxi). The Xiongnu regrouped and deployed their forces northwest of Loufan, but were once again routed by Liu Bang's cavalry. A string of victories made Liu Bang complacent, fostering arrogance and underestimation of the enemy. At that time, the Xiongnu army had retreated to Daigu (between present-day Fanshi and Yuanping, Shanxi), while Liu Bang's forces were stationed at Jinyang. After several fierce battles, Liu Bang believed the Xiongnu's strength had greatly diminished and planned to wipe them out in one final push. Before launching the attack, he wanted to assess the Xiongnu's current situation, so he sent several scouts to the front lines. However, Modu Chanyu got wind of this and hid all the elite Xiongnu soldiers in the rear, placing only weak and inexperienced troops at the front. When the scouts saw this, they eagerly returned to report to Liu Bang, all urging an immediate attack. Liu Bang then decided to send Liu Jing to verify the situation. Upon his return, Liu Jing told Liu Bang, "The Xiongnu army indeed appears weak, but Modu Chanyu must have hidden his elite forces to deliberately mislead us. I believe the Han army should not act rashly." Liu Bang was displeased and immediately scolded Liu Jing for being cowardly and undermining morale. He ordered Liu Jing imprisoned in Guangwu's jail, to be dealt with after defeating the Xiongnu.
Liu Bang first led a cavalry unit to rush to Pingcheng (present-day north of Lingchuan, Shanxi) to prepare for battle before the infantry arrived, so that combat could begin once they joined. When the cavalry reached White Mountain, the Xiongnu army ambushed them, blocking their path from both front and rear, trapping the Han forces completely. The cavalry had only brought a small amount of provisions, and the infantry could not arrive in time to provide support. Liu Bang ordered several assaults, but none broke the encirclement. Modu Chanyu divided his troops into four groups, surrounding the Han army from all directions and launching attacks in rotation. After several rounds, both sides suffered heavy casualties, but neither could overpower the other. The northern winter was bitterly cold, and the Han soldiers, being from the south, could not withstand the freezing temperatures; many suffered varying degrees of frostbite, with some losing fingers to the cold. Although the Xiongnu army had ample supplies and equipment, the Han troops fought to the death, leaving no opening for their enemy to exploit.
The two armies faced off at White Mountain for seven days, leaving Liu Bang deeply worried as he sought advice from his generals on how to break the siege. Chen Ping told Liu Bang that Modu Chanyu was especially fond of his consort, the Yanzhi, and suggested sending an envoy with gold, silver, and jewels to bribe her, hoping she might persuade the Chanyu to withdraw. Liu Bang agreed, and Chen Ping, along with another general, secretly slipped into the Xiongnu camp carrying jewelry and a scroll painting of a beautiful woman. They found the Yanzhi, presented her with the jewels and the painting, and promised that if the Xiongnu retreated, they would offer even more treasures and present the woman in the painting to the Chanyu. The Yanzhi joyfully accepted the jewelry, but when she saw the painting, she feared that if such a beauty were given to the Chanyu, she would lose his favor. So she agreed to persuade Modu Chanyu to spare the Han emperor and asked Chen Ping to take back the painting. That night, the Yanzhi said to Modu Chanyu, "The two armies have fought without a clear victor, and both sides have suffered losses. Even if the Chanyu were to take the Central Plains, we could never adapt to the life and food there—why must we contend with the Han? Besides, the Han emperor has been trapped for days without serious harm, which surely means he has divine aid. It would be best for the Chanyu to let them go." Modu Chanyu was skeptical but went to observe the Han camp the next day. Seeing no signs of panic, he believed the Yanzhi's words and ordered a partial withdrawal, allowing Liu Bang to break out of the siege. Liu Bang led his cavalry in a hasty escape through the gap in the Xiongnu lines. Upon returning to the capital, his first act was to execute all those who had previously urged him to attack the Xiongnu. He then released Liu Jing from prison, enfeoffed him as the Marquis of Guannei, and granted him a substantial reward.
Although Modu Chanyu had released Liu Bang, he continued to harass the towns along the northern border. Liu Jing suggested that Emperor Gaozu of Han marry a princess to the Chanyu to maintain border stability through a policy of peace through marriage. Lü Zhi refused to let her daughter go, so Liu Bang found a substitute girl to marry Modu Chanyu, sending her north with large quantities of gold, silver, and cloth, escorted by Liu Jing, while also promising to send the Xiongnu a fixed amount of grain and daily necessities each year. This measure eased tensions between the Han Dynasty and the Xiongnu, sparing the Han people the suffering of war.