Why are Chinese claiming most of the South China Sea?

(Image: Brian Stauffer)

As early as 2014 the American Atlanticist publication The Atlantic began worrying aloud about aggressive Chinese actions to reclaim spits of land in the seas used by nearby nations: 

The country's intensifying efforts to redraw maritime borders have its neighbors, and the U.S., fearing war. But does the aggression reflect a government growing in power — or one facing a crisis of legitimacy?  

The Atlantic was not alone in wondering about the impetus for Chinese maritime aggression; by now an entire genre of defense analysis has materialized to ponder such weighty issues as The Nine Dash Line, the physical shoves given by Chinese officials to American counterparts during at least one high-level defense meeting earlier this year -- and the all-important question, Whatever happened to Peaceful Rising?  

Those are typical questions about China from Westerners and particularly Americans, who are reluctant to believe anything is happening with foreign countries unless they first know why. But all right, here's why, from a noted Thai defense expert: perhaps her analysis can be included in the next U.S. Defense Intelligence Agency Worldwide Threat Assessment. 

Now regarding the reason for China's specific efforts to convert rocks in the sea to military bases: