Lý Thường Kiệt had fought a war with the Cham in 1069, and in 1076 Song called on the Khmer Empire and Champa to go to war again in 1076. At the same time, the Song commander Guo Kui (1022–1088) led the combined Song force of approximately 100,000 men against Dai Viet. The Song quickly regained Quảng Nguyên prefecture and in the process captured the resistance leader Lưu Ký. By 1077, the Song had destroyed two other Vietnamese armies and marched towards their capital at Thăng Long (modern Hanoi). Song forces halted at the Nhu Nguyệt River (in modern Bắc Ninh Province), where Lý Thường Kiệt had defensive ramparts built on the southern banks. However, Song forces broke through his defense line and their cavalry advanced to within several kilometers of the capital city. The Vietnamese counterattacked and pushed Song forces back across the river while their coastal defenses distracted the Song navy. Lý Thường Kiệt also launched an offensive, but lost two Vietnamese princes in the fighting at Kháo Túc River. According to Chinese sources, "tropical climate and rampant disease" severely weakened Song's military forces while the Vietnamese court feared the result of a prolonged war so close to the capital. In 1078 China defeated Đại Việt and overran several districts that would later make up part of Cao Bằng Province.