How was Qin Shi Huangdi able to unite China and keep it united during his lifetime?

Qin Shi Huangdi was able to unite China and keep it united during his lifetime because of his fear as an emperor and his bureaucracy.

Explanation:

Qin Shi Huangdi was the first ruler of a unified China. It was he that began his empire in Qin and from then on conquered the territories in the land of China one by one and then unified them under one large empire.

His status as a formidable general at war and a more formidable statesman made it harder for any state to try to recede his empire as his policies prevented such attempts.

It was also a matter of general prosperity which increased in his time as more and more populace became happy under his rule.