The Island of Yap is a small island located in the center of the Pacific Ocean, mostly famous today for its use of massive stones as a form of currency, in 1922 it represented an unusual nexus point of history and around it circled a vast series of diplomatic maneuvers between the United States, Great Britain, and Japan. The surface issues was over Japan’s control of the valuable underseas cables that came ashore on Yap Island, cables that the United States relied upon to maintain reliable fast communications between its mainland and the US occupied Philippine Islands. But beneath this surface issue was a deeper concern, the serious concern with the U.S. State Department about the remote, but real, possibility of the U.S. being drawn into a two front war over Yap Island, with the US in the center of a Japanese-British beat-down sandwich. The heart of the issue was an old alliance signed in 1902, and renewed annually, between Great Britain and Japan that promised mutual defense in the event of war being declared on either party. The Japanese had joined World War I due to this treaty and dutifully waged war on Germany, and in 1922 the treaty was coming up once again for renewal. Japan was eager to renew it and Great Britain was hesitant, it wanted to build on its growing relationship with the U.S. after World War I and the idea that an old treaty might force it to attack the U.S. didn’t sit well with that goal. In turn the U.S. was not looking forward to the idea that if it wanted a good solid war with Japan over an issue in the Pacific, like Yap Island, that it had to worry about Great Britain attacking the U.S. east coast or other odd scenarios, like an invasion from Canada into the U.S. Northwest. No what was needed was a new means of breaking the Anglo-Japanese Alliance apart but it had to be done in a manner with finesse.
The problem for Great Britain was the Anglo-Japanese Alliance was still looked upon favorably by the British public and Britain’s leadership felt that breaking an alliance with a partner nation with whom they had just fought a successful war would be a major diplomatic black mark. Furthermore, Japan was so eager to renew the alliance in 1922 on general principle that Britain’s leaders felt something had to be done to appease Japan or they risked losing a valuable ally and possibly gaining an angry adversary who could threaten their position in Asia. The end result was the creation of a new alliance, the Four Power Treaty of 1922. What this treaty did was replace the formal Anglo-Japanese alliance with a treaty that promised mediation, and recognition of the current division of territories in the Pacific, between the United States, Great Britain, and Japan. The treaty also involved France which was dropped into the proceedings to round out the treaty and put a “neutral” power into the mix. At the same time the US and Japan hammered out a treaty about Yap Island, Japan kept the island but the US got protected commercial interests on the island. It was not the treaty Japan wanted but it was one they could settle on, as the Four Power Treaty was also one that Japan didn’t want, but settled on.
You might ask what Japan got in exchange for those two concessions that made it so willing to swallow two less-than-optimal treaties, well first it got huge gains in the Nine Power Treaty over China, a topic too broad for this post but good for one in the future. More critically though it gained a major concession in the 1922 Washington Naval Treaty, technical naval parity with Great Britain and the United States in the Pacific. Prior to the Washington Naval Treaty the general theory was that each nation would attempt to build the largest navy it could in an effort to defend its own interests and to be able to project successful offensive power against an opponent. The Washington Naval Treaty attempted to end the second aspect of naval building by instead creating strict fleet number and tonnage ratios – ratios designed to allow a power to defend its regional or global interests successfully but leave it lacking enough naval force to act offensively, in theory ending aggressive war. Japan was granted naval parity with the United States and Great Britain in the Pacific, meaning that although it’s fleet was smaller in tonnage and number than the US and British fleets, within its zone in the Pacific it was felt Japan’s fleet was sufficient to ensure no other power could challenge it. Which, in turn, was a defacto granting to Japan of something it had coveted since the turn of the early 20th century, equality with Europe’s great powers. (It was an added ego rub that Japan’s fleet was larger than that of France or Italy.)