Furthermore, the loss of control over the fertile southern grassland meant that Xiongnu had to hole up in the cold, barren land of the northern Gobi Desert and Siberia, struggling to survive. As a result, there was a true truce between the Han Dynasty and Xiongnu for seven years, which ended after a Xiongnu raid in 112 BC at Wuyuan. The Xiongnu, however, never recovered to the strength of their past glory days, and would break apart into smaller clans in the coming decades, ultimately splitting into Southern and Northern branches after a century later, as the Southern branches become the subordinates of the Han Dynasty. With the Northern branches being under attack from the southern branches, the Han empire and other Nomadic tribes such as the Wuhuan and Xianbei, gain independence from the Xiongnu overlords, forcing the Northern branches to immigrate westward. Eventually, the fleeing Northern branches of Xiongnu became the ancestors of the Huns, which would cause indirect destruction and dissolution of the Western Roman Empire in the following centuries. While others migrated south of central Asia becoming the Xionites, Kidarites, Hephthalites and Nezak Huns, indirectly causing the collapse of the Gupta Empire, and becoming a major burden to the Sassanid Empire.