Su Wu
Emperor Wu also made attempts to try to intimidate Xiongnu into submission, but even though peace negotiations were ongoing, Xiongnu never actually submitted to becoming a Han vassal during Emperor Wu's reign. In 103 BC, Chanyu Er surrounded Zhao Ponu and captured his entire army – the first major Xiongnu victory since Wei Qing and Huo Qubing nearly captured the chanyu in 119 BC. Following Han's victory over Dayuan in 102 BC, however, Xiongnu became concerned that Han could then concentrate against it, and made peace overtures. Peace negotiations failed when the Han deputy ambassador Zhang Sheng (张胜) was discovered to have conspired to assassinate Chanyu Qiedihou (且鞮侯). The ambassador, the later-famed Su Wu, would be detained for two decades. In 99 BC, Emperor Wu commissioned another expedition force aimed at crushing Xiongnu, but both prongs of the expedition force failed. Li Guangli's force became trapped but was able to free itself and withdraw, while Li Ling, Li Guang's grandson, surrendered at the end after being surrounded by Xiongnu forces. One year later, receiving a report that Li Ling was training Xiongnu soldiers, Emperor Wu had Li's clan executed.