Okinawa is “the keystone of the Pacific.” I’m not entirely sure exactly, with today’s technology and all, if the Ryukyu Islands are as strategically important as they one were, but as late as the Cold War, American strategists considered Okinawa crucial to maintaining America’s control of the Pacific. Before that, Sec. of State Acheson made a fateful speech at the Washington Press Club outlining American’s “defensive perimeter” that ran from the Aleutians, down through the Japanese home islands and Ryukyus, to the Philippines (omitting both Korea and Taiwan in the process, months before the Korean invasion).
I do know today that the waters off Mainland China are relatively very shallow, making submarines easier to detect as they pass by the chain of islands from Kyushu to Taiwan. Some experts believe that China is paranoid about being boxed in by the US and is seeking a larger and more modern Pacific fleet.