Under what conditions did qin take the thrown

Do you mean throne? 
At the age of thirteen, he succeeded his father's regality. Ying Zheng was very aggressive and ambitious at an early age. He assumed full power at 22 by ridding himself of his premier, Lu Buwei, who acted as regent while he was a minor.

I am not really sure what you mean. Like which Qin are you talking about?

It covered the territory of land across eurasia from northeastern europe to the pacific ocean.