ChocolatePancake is perfectly right.
See Pacific 2nd Ed. rulebook, top of page 9:
These two powers [UK and ANZAC]
also have an arrangement with the
Dutch government in exile (Holland having been captured
by Germany) and have taken guardianship of the Dutch
territories in the Pacific. As a result, they are free to move
units into these territories as a noncombat movement at any
time, as long as they have not yet been captured by Japan.
They may actually take control of them (gaining their IPC
income) by moving land units into them. Additionally, the
United Kingdom and ANZAC consider attacks against any
Dutch territories to be acts of war against them directly.
Once a Dutch territory has been captured by Japan,
however, it may be captured and controlled by any power.