Partition of Jin
After the great age of Jin power, the Jin dukes began to lose authority over their nobles. A full-scale civil war between 497 and 453 BC ended with the elimination of most noble lines; the remaining aristocratic families divided Jin into three successor states: Han, Wei, and Zhao.
With the absorption of most smaller states in the era, this partitioning left seven major states in the Zhou world: the three fragments of Jin, the three remaining great powers of Qin, Chu and Qi, and the weaker state of Yan near modern Beijing. The partition of Jin, along with the Usurpation of Qi by Tian, marks the beginning of the Warring States Period.
Read more about this topic: Spring And Autumn Period