In 230 BC, King Zheng unleashed the final campaigns of the Warring States period, setting out to conquer the remaining independent kingdoms, one by one.
The first state to fall was Hán (韓; sometimes called Hann to distinguish it from the Hàn 漢 of Han dynasty), in 230 BC. Then Qin took advantage of natural disasters in 229 BC to invade and conquer Zhào, where Qin Shi Huang had been born. He now avenged his poor treatment as a child hostage there, seeking out and killing his enemies.
Qin armies conquered the state of Zhao in 228 BC, the northern country of Yan in 226 BC, the small state of Wei in 225 BC, and the largest state and greatest challenge, Chu, in 223 BC.
In 222 BC, the last remnants of Yan and the royal family were captured in Liaodong in the northeast. The only independent country left was now state of Qi, in the far east, what is now the Shandong peninsula. Terrified, the young king of Qi sent 200,000 people to defend his western borders. In 221 BC, the Qin armies invaded from the north, captured the king, and annexed Qi. Some of the strategies Qin used to unify China were to standardize the trade and communication, currency and language.
For the first time, (nearly) all of China was unified under one powerful ruler. In that same year, King Zheng proclaimed himself the “First Emperor” (始皇帝, Shǐ Huángdì), no longer a king in the old sense and now far surpassing the achievements of the old Zhou Dynasty rulers. The emperor made the He Shi Bi into the Imperial Seal, known as the “Heirloom Seal of the Realm”. The words, “Having received the Mandate from Heaven, may (the emperor) lead a long and prosperous life.” (受命於天，既壽永昌) were written by Prime Minister Li Si, and carved onto the seal by Sun Shou. The Seal was later passed from emperor to emperor for generations to come.
In the South, military expansion in the form of campaigns against the Yue tribes continued during his reign, with various regions being annexed to what is now Guangdong province and part of today’s Vietnam.