The Papahānaumokuākea Marine National Monument has been in the news recently as President Obama expanded the size of the protected area. This National Monument extends northwest from Hawaii along a string of small islands.
So what do islands near Hawaii have to do with China? China and other nations in the area have been arguing over the ownership of several groups of small islands and reefs. Much of the debate is over the exact nature of the islands since this determiens the amount of territory around the islands which can be claimed by the country as territorial waters or an exclusive economic zone.
In reading news stories it appears that whether islands are inhabited, whether they are above water all the time (or only at high tide) and similar factors are involved. Truly territorial waters are best enforced for inhabited islands.
Now look at the National Monument near Hawaii. As far as I can tell few of the islands are inhabited yet by declaring a National Monument the US is expressing an exclusive economic zone out 200 miles from these islands (a map shows the monument to be roughly a 400 mile wide by 1000 mile long region).
While there are no nearby nations to dispute the US ownership of these islands, I can imagine the controversy if some nation tried to fish in the region and disputed the US claim to this wide an area. Claiming this much territory around uninhabited islands could provide a precedent for China or another nation making claims to islands off their own coasts.