Guam figures heavily into announced Chinese naval strategy. They have laid out by decade when they plan to push their seapower out to the "inner" and "outer" island chains. Guam is the key to the outer chain. It has the biggest all weather port between Pearl and Manila, weapons depots for the Navy and AF, B-52 runways, sub bases, etc etc etc.
It is directly under the Chinese cross-hairs. It is the key to any American defense of the Western Pacific.
They are all critical and they all represent stepping stones in increasing distance away from Mianland China...and they are all critical to the Red Chinese goals, that they have stated themselves, in exerting their influence and control out past the outer island chain into the Pacific.
In The Dragon's Fury Series, the execute a brilliant, long-term plan to achieve that control by misdirecting us, "sharing" with us, bribery, blackmail, murder and ultimatel military action when we are in a position to succumb to it...that we then spend several years fighting to reaquire.