Why are dynasties important in Chinese history?
Dynasties were China's first settlers. Dynasties were nomadic warlords who led China.
Dynasties are unchanging landmarks. Dynasties ruled China over long periods of time.
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D - Dynasties ruled China over long periods of time.

Explanation:

A dynasty is a succession of rulers of the same line of descent who would rule for long periods of time. Most dynasties in China ruled for thousands of years.

i think the answer to your question is: settlement of the interior and economic growth. ( ^_^)／