Complex sentence: The Han army crushed the rebellion, and the Dongyue kingdom began to fragment after King Yushan stubbornly refused to surrender: elements of its own army defected and turned against their ruler.
Split into simpler sentences: The Han army crushed the rebellion, and the Dongyue kingdom began to fragment after King Yushan stubbornly refused to surrender. Elements of the Dongyue army defected and turned against their ruler.