Warring States refers to the historical period when the seven states were in fight with each other. It was an era of turmoil.
During Warring States, the seven fighting states were in fact only the larger ones among all states. There were still smaller states including Zhou, Lu, Wei, and Zheng, and many ethnic groups such as Hun and Donghu in the north, Baiyue in the south, and Bashu in the southwest. But later they were gradually conquered and annexed by those larger states.
Warring States can be divided into three stages. The first stage refers to 475 BC—338BC when Shang Yang (Councilor-in-chief in State of Qin) was killed. In order to become much stronger and more prosperous, each country made efforts to conduct various reforms, and the famous ones included reforms carried out by Shang Yang in Qin, reforms proceeded by Wu Qi in Chu, and reforms conducted by Li Li in Wei. Therefore social condition in the first stage was relatively stable.
The second stage was from 338 BC to 288 BC when Qi and Qin agreed to be the ruling states together. In 284 BC, the six larger states joined together to attack Qi. Each state increased its military spending and opened the arm race with each other. Wars were frequent in this period. The larger states conquered the smaller ones and finally became seven strong states. In 288 BC, Qin and Qi were respectively known as West Empire and East Empire, and the fight between the two grew more intense.
In the third stage from 284 BC to 221 BC, Qin finally annexed the other six states and unified China Proper for the first time.