What was a good warfare era for China and why?

A very good warfare era from ancient China was the Warring States era from 475 to 221 B.C.  They had seven very good warfare kingdoms also.  It was also one of the best warfare eras of its times before it and developed the military weapon the double edged sword.  They also used the crossbow and adopted the cavalry warhorse and riding trousers from the Steppe barbarians.  Another thing is that iron working appeared too.  They also used chariots, crossbows, and catapults even though my personal favorite is the chariot which I think is pretty cool.  They also were in the battle of Guiling and used the double pronged spear and a dagger axe with a knife at the end of it.  That is why the Warring States era was one of the best warfare eras.