Before the Warring states, the Shang dynasty that controlled more area than Zhou was much more powerful than the Zhou dynasty which let all those pretty much independent states to exist within its kingdom. As before the Shang, these was the Xia dynasty which also administered larger area than the Zhou according history. Right up to the Yellow emperor and beyond, different groups of Chinese within China basically had been trading, mixing and exchanging cultures right up to the neolithic times as shown by the poetry and artifacts they produced, that is areas like Inner Mongolia, Liaoning and Yangtze river areas have lots connections with central China at the time.
As for Xinjiang, Han Chinese have settled there I say at least 5000 years ago, the people there have at least a third of genetics that are the same to East Asians or Han Chinese, people there also practice many Han Chinese traditions too such as eat Han Chinese foods and use chopsticks. Two thousands years ago, the area came under Chinese gov control becos it necessitate the Chinese to do so in order to save the Chinese nation from Hun plundering and invasion, China's existential survival was at stake, and this can't be said of say Greek and Britain when they expanded and conquered other people.
As for Tibet, the people there are closely related to Han Chinese with almost identical genetic makeups, they only split from Han Chinese just few thousands years ago. Both Tibetans and Han Chinese were use to be Buddhists. It was the Mongol and Manchu minorities who extended Chinese control to the area first, not Han Chinese, there are some differences.
I am not saying that Chinese nation didn't expand in any size for the last thousands years, but, China is/was basically not an expansionist nation or empire in nature esp when you compare it to the typical well known world empires such as the Hellenic empire, British empire, Ottoman empire and Mongol empire in the past.
Maybe will perish.