The Washington Naval Conference of 1921 (which actually lasted into 1922) was a meeting that was meant to produce a disarmament treaty or at least a treat that would limit naval weapons in the Pacific.
The most important treaty that came out of this, in my mind, was the Four Power Treaty. This treaty was made between the US, Japan, Great Britain, and France.
These countries were all important because they had major interests in the Pacific (and especially the Western Pacific). Japan was seen as the most likely enemy for the US in the Pacific.