After 622 BC, Chu forced the remaining states along the middle Huai River into vassalage, destroying any of them that continued open resistance. It also concluded a pact with Wu and Yue, "which kept them from wooing the Shu states for a quarter century". As result, Chu became the unchallenged ruler of most of the Huai River valley, so that Xu increasingly fell under Chu's influence as well. Despite this, the extremely weakened kingdom continued to conspire with other states against Chu. In 620 BC, Xu undertook a campaign against Ju in Shandong. Chu's dominance over the Huai River valley was broken in 584 BC, when Wu launched a large-scale western offensive, during which Xu was also attacked by Wu forces. From then on, Wu and Chu constantly fought each other for supremacy over the Huai River valley. Xu found itself under pressure by both of these powerful states. Even though its political powers were further weakened, it experienced its cultural zenith during this period. Since 542 BC, Xu became inclined to side against Chu with Wu in order to regain its full independence, with King Yichu marrying a Wu princess. This new alliance resulted in grave consequences for Xu in 539 BC. In that year, King Ling of Chu called for meeting of the states at the former capital of Shen, wanting them to accept him as new hegemon of China. Although hostile to Chu, Xu's ruler was obliged to be present at the meeting as he feared a possible retaliation. At Shen, however, Chu's ruler had Yichu seized because of his close connections to Wu. He then compelled Xu to participate in an invasion of Wu in 537 BC. One year later, King Yichu escaped and returned to his capital. King Ling of Chu, fearing that Xu would revolt, promptly invaded the small kingdom. Wu came to Xu's aid, however, and defeated Chu's army. Afterwards, Xu openly aligned itself with Wu. In winter 530 BC, King Ling of Chu led another army to besiege and conquer Xu's capital in order to prepare an invasion of Wu. The siege lasted until the next summer, when Zi'ao launched a coup at Ying and took control of Chu's government. King Ling's army then almost completely deserted him, while the remaining loyal troops broke off the siege of Xu and began to retreat to Chu, only to be overwhelmed and destroyed by an army of Wu at Yuzhang. In 526 BC, Duke Jing of Qi wanted to restore Qi's old hegemony, and launched an invasion of Xu.