In the spring of 1114, Aguda united the Jurchen tribes under his leadership and started a rebellion against the Liao dynasty. In 1117, after the Jurchens had conquered several Liao cities, Aguda declared himself emperor and established the Jin dynasty. In December 1121, Wuzhu, then a teenager, participated in battle against Liao forces. When the Jurchens received news that the Liao ruler, Emperor Tianzuo, was out on a hunting expedition at Yuanyang Lake (鴛鴦濼; northwest of present-day Zhangbei County, Hebei Province), Wolibu (斡離不; Wanyan Zongwang) and Wuzhu led an army to attack the Liao emperor in the hope of catching him off guard. During the battle, Wuzhu, after expending all his arrows, seized a Liao soldier's weapon and continued fighting. He killed eight enemy soldiers and captured five, and became famous after the battle. By 1124, the Liao dynasty had lost most of its territories to the Jurchens. On 26 March 1125, Emperor Tianzuo was captured by Jin forces led by Wanyan Loushi (完顏婁室) in Yingzhou (應州; in present-day northern Shanxi Province). Months later, he was sent to the Jin capital in Shangjing (上京; present-day Acheng District, Harbin, Heilongjiang Province). Wuzhu participated in the Jin–Song Wars, which broke out in 1125 between the Jin dynasty and the Han Chinese-led Northern Song dynasty. He served as an officer in the Jin dynasty's Eastern Army, which was commanded by his second brother, Wolibu (斡離不; Wanyan Zongwang), who held the appointment of Right Vice-Marshal (右副元帥). In the first month of 1126, Wolibu sent Wuzhu to attack Tangyin County; Wuzhu won the battle and forced the 3,000 Song defenders to surrender. Soon after, the Eastern Army reached the Yellow River and attempted to cross, but the Song forces had already set the pontoon bridges on fire. The Jin officer Helusuo (合魯索) led 70 horsemen to cross the river at a shallow point and killed 500 Song soldiers burning the bridges. Wolibu sent Wu Xiaomin (吳孝民) as a messenger to the Song capital, Bianjing (present-day Kaifeng, Henan Province), to admonish the Song dynasty for breaking its earlier alliance with the Jin dynasty.