attack Puban (蒲阪, in modern Yuncheng, Shanxi) and Pu Ji (普幾) to attack Shancheng (陝城, in modern Sanmenxia, Henan), while himself making a fast, cavalry-based attack on the Xia's heavily fortified capital Tongwan (統萬, in modern Yulin, Shaanxi). Catching the Xia emperor Helian Chang by surprise, the Northern Wei troops intruded into Tongwan before withdrawing with much loot, while in the south, Helian Chang's generals Helian Yidou (赫連乙斗) and Helian Zhuxing (赫連助興) abandoned not only Puban, but also Chang'an, allowing Daxi to occupy the Guanzhong region. In spring 427, Helian Chang sent his brother Helian Ding south to try to recapture Chang'an, but Helian Ding's forces became stalemated with Daxi's. In response, Emperor Taiwu made another attack on Tongwan. Helian Chang initially took Helian Ding's suggestion to try to defend Tongwan until he could defeat Daxi, but misinformation that Helian Chang received then induced him to come out of Tongwan to engage Northern Wei forces. Emperor Taiwu defeated him in battle, causing him to be unable to return to Tongwan and forcing him to flee to Shanggui (上邽, in modern Tianshui, Gansu), allowing Emperor Taiwu to capture Tongwan. In the start of what would be a string of marriages that could be characterized as either politically- or trophy-taking-related, he took three of Helian Bobo's daughters as his concubines. Upon hearing of Tongwan's fall, Helian Ding disengaged from Daxi and joined Helian Chang at Shanggui as well. In 428, Daxi and Qiudun Dui, trying to capture Helian Chang, instead became trapped by Helian Chang in the city of Anding (安定, in modern Pingliang, Gansu). However, Daxi's subordinates Yuchi Juan (尉遲眷) and Anchi Jia (安遲頡) made a surprise attack and captured Helian Chang. Helian Ding took over as the emperor of Xia. Meanwhile, Emperor Taiwu treated Helian Chang as an honored guest, supplying Helian Chang with the same supplies that he himself used, and he married his sister Princess to Helian Chang and created him the Duke of Kuaiji; he also rewarded Yuchi and Anchi greatly and created them dukes. Subsequently, Daxi, humiliated that his subordinates captured Helian Chang and he himself appeared helpless, aggressively pursued Helian Ding, but instead was defeated and captured by Helian Ding. In fear, Qiudun and Tuoba Li (拓拔禮) the Prince of Gaoliang abandoned Chang'an as well and fled to Puban, allowing Xia to recapture Chang'an. In anger, although Qiudun had been a high-level official for him