The main reason Chinse are interested in 9 dotted lines are the US presence in Malacca strait. If US leaves then the importance of 9 dotted lines will cease and PH will get back its freedom of navigation through dotted lines.
This is like saying that if the police leave, there will no longer be any criminals.
No...I am
NOT saying China is the criminal and the US is the policeman.
NOT saying so.
What I am saying is that you showed a serious lack of understanding of the use and display of power in inter-state relationships, namely, the absence of a power does not equate to the absence of those who would seek to dominate.
The goal of any country is to ensure its own survival and there is nothing more assured of that than sheer physical power. Restrained, maybe. But there is no substitute for physical power. Even the ability to inflict damages, if not outright victory, is enough as a deterrence factor. Most modern states are comfortable with the idea that all they need is enough power to inflict damages, not conquering, power. See European Union.
But for a state that feels there is a need to project, if not actually have, overwhelming physical power over its immediate neighbors, the absence of a current dominant power is nothing but an invitation to become that dominant power and to work hard to assure that status for as long as possible.
The US did nothing to introduce and nurture in China the seed of the idea of the need for a Chinese dominance in Asia. That was done by the Europeans when they carved up China for their own interests. Next was the Japanese when they invaded mainland China and took over Manchuria. If anything, it was the US who had no colonial interests in mainland China and who helped the Chinese against Imperial Japan in WW II.
What motivated China to work to become the dominant Asian power was that 'hundred yrs of humiliation' produced by the Europeans, and now, since there is a status quo, an equilibrium of physical prowess among the Asian states, an inter-states condition that was majorly affected by the US from the end of WW II and throughout the Cold War, China is able to become that dominant power regardless of whether there is a US presence or not.
Let me put it this way...Even if I live in a gated neighborhood patrolled by our own security forces, that does not mean I should not have locks on my doors. Likewise, if there is no apparent challenges to my aspiration to be the dominant force in my neighborhood, that does not mean I should not become that dominant force. If an opportunity arise -- take it. My survival may not have been threatened before, but now my survival is even more assured in spite of a current security force.