春秋五霸
At the same time, the northward expansion of the State of Chu was also resisted by Duke Wen; the two states' conflict was mostly played out among the smaller states which lay between their territories and formed alliances with one state or another. In 633 BC, Chu invaded the State of Song, which was an ally of Jin; Duke Wen led his coalition, including troops from Qin, Qi and Song, and won a decisive victory over Chu forces at the Battle of Chengpu in 632 BC. This battle checked Chu's northern expansion for decades, while cementing Duke Wen's position; the next year, he convened a large coalition of rulers at Jiantu, and was confirmed as hegemon over the other states, becoming one of the Five Hegemons.