How were the qing dynasty able to take over China?

According to my reading, I think the reason can be analyse from two aspects: the reason from Ming Dynasty and the reason from Qing Dynasty.
In late Ming Dynasty, the government is decayed and the army is poor, so it could not contend against the strong army from Manchu. Besides, the general of Ming Dynasty is not so good as Manchu did.
After a series of failures of war, the Manchu eagerly want to be succesful in the war and they adjust their tatics, so that they can win in the end.
Due to the two reasons above, the Qing Dynasty took over China.

They were able to take over the Ming Dynasty by war I believe.

Qing did not take over intially. The Ming fell after a warlord (Li Zhicheng) invaded the imperial palace. A general in order to seek revenge against Li open the gates of the great wall to allow the Qing to drive out Li. But the Qing did not leave after that and that's how they won.