Why the win dynasty fell

In 207 BCE, Qin Shi Huang's son was killed, and the dynasty collapsed entirely.

Explanation:

Qin Shi Huang was paranoid about his death, and because of this he was able to survive numerous assassination attempts.

(He became increasingly obsessed with immortality and employed many alchemists and sorcerers. Ironically, he ultimately died by poisoning in 210 BCE, when he drank an "immortality potion.")