State of Qin
The Qin State is the strongest and indisputable.
The State of Qin became the final victor of this era.
Chu
The State of Qin suffered its only major defeat in the War to Unify the State of Chu. The State of Chu is located in the fertile land of the south. According to historical records, as many as 500,000 troops were stationed. It would take more than a year or two for the State of Qin to completely defeat the State of Chu. Therefore, it won second place without dispute.
Zhao Guo
Although he lost the Battle of Changping and almost completely destroyed his army, he defeated the invasions of other countries many times and became one of the countries that troubled the Qin state the most. This is because Zhao Guo has excellent generals. Qin Shi Huang sent troops to attack Zhao. But he was repeatedly stopped by Zhao's general Li Mu. The King of Qin had to use treachery to bribe Zhao's courtiers and spread rumors that Li Mu might rebel. King Zhao planned and killed Li Mu. Subsequently, the state of Zhao was destroyed. It took more than a year for the State of Qin to destroy the State of Zhao and destroy the remnants of the State of Zhao.
Qi State
The State of Qi was a superpower during the Warring States period. However, it was defeated by the Gan coalition. After the Qi state recovered almost all of the lost territory in Tian Dan , it began to implement a policy of isolation and allied itself with the Qin state. Why did I put the State of Qi in fourth place, because the State of Qi had the potential (more and better land and army) to fight the State of Qin better than the three countries below, but they did not do so. Ironically, the State of Qi was the last country to fall without a war.
Yan Guo
The Kingdom of Yan is a northern country. Its capital was located in present-day Beijing. The lands of the Yan kingdom were not plundered by the Qin state like Han and Wei. It can send many troops. However, the Yan Kingdom is small in size and faces the threat of northern nomads. After Jing Ke's defeat in assassinating the King of Qin, the Yan kingdom perished.
Wei
The Wei state had a close relationship with the Qin state. Its land has been at war with the Qin state many times. The State of Qin acquired many lands of the State of Wei and approached the capital of the State of Wei. Wei did play well at the last minute, though. The Qin general Wang Ban had to attack the city by a water army.
Han Guo
Undoubtedly the weakest. Over the past hundred years, it has shrunk significantly. This is the smallest state with the least population. In the end, the Qin state surrendered without a fight and annexed all the territory of the Han Dynasty.