In 1209, Wanyan Yongji usurped the Jin throne. He had previously served on the steppe frontier and Genghis greatly disliked him. When Yongji demanded tribute in 1210, Genghis openly defied him, setting the stage for war. Despite the possibility of being outnumbered eight-to-one by 600,000 Jin soldiers, Genghis had made preparations for an invasion since 1206 due to Jin vulnerabilities. Genghis had two aims: to take vengeance for past wrongs committed by the Jin, foremost among which was the death of Ambaghai Khan in the mid-12th century, and to win the vast amounts of plunder his troops and vassals expected.

In March 1211, after organizing a kurultai, Genghis Khan initiated his invasion of Jin China, swiftly reaching and bypassing the Jin's border defenses with help from the Ongud tribe in June. The invasion strategy focused on widespread plundering and burning to undercut Jin resources and legitimacy while aiming to control strategic mountain passes for further advances. The Jin faced significant territorial losses and a wave of defections, notably contributing to Muqali's significant victory at Huan'erzhui in late 1211. However, the campaign paused in 1212 due to Genghis being injured by an arrow during the siege of Xijing. This setback led him to establish a specialized siege engineering unit, incorporating 500 Jin specialists to enhance his military capabilities.

By 1213, the Mongols overcame the strengthened Juyong Pass defenses, led by Jebe, creating a pathway to Zhongdu (now Beijing). The Jin's political structure weakened significantly when the Khitans rebelled and Hushahu, the military leader in Xijing, executed a coup, killing Yongji and installing Xuanzong as a puppet leader. Despite their initial success, Genghis's army faced setbacks, including disease and food shortages, leading to dire conditions and peace negotiations. Genghis managed to extract substantial tribute from the Jin, including horses, slaves, a princess, and valuable goods, then retreated in May 1214.

After the northern Jin regions were devastated, Xuanzong relocated the capital to Kaifeng, a move Genghis Khan viewed as a breach of their peace treaty, prompting him to plan another attack on Zhongdu. Historian Christopher Atwood notes that this decision marked Genghis's commitment to conquer northern China. Throughout the winter of 1214–15, Muqali successfully took over many towns, leading to Zhongdu's surrender in May 1215, though the city faced looting. Genghis returned to Mongolia in 1216, leaving Muqali to oversee operations in China, where he continued to challenge the Jin until his death in 1223.