Incentives for war during the warring states period

Feb 2017
I've been reading about the Warring States Period in 'Early China' by Li Feng and a few things weren't too clear when I read it:

- what were the incentives for each state to be at war?

- was there a reason why the states couldn't have remained peaceful?

And I'll throw this one in here for fun:

- was the situation in China at the time somewhat analogous to warfare in Medieval Europe?