Qin did not immigrate to Xinjiang.

To understand this, we must first understand how big the territory of China was when the Zhou Dynasty was unified.

Xinjiang at that time was a foreign country. The land is vast and sparsely populated, and the main concentrated tribes are Xiongnu and Rongdi. Sometimes they invade China through Yinshan grassland.

Therefore, after the reunification of Qin, the Great Wall will be built all the way to Gansu, because the northern and western parts of Jiayuguan were not part of Chinese territory at that time.