The Washington Naval Conference, was a disarmament conference called by The United States and held in Washington, D.C., from November 12, 1921 to February 6, 1922. It was conducted outside the auspice of the League of Nations. It was attended by nine nations--the United States, Japan, China, France, Britain, Italy, Belgium, Netherlands, and Portugal--regarding interests in the Pacific Ocean and East Asia. Soviet Russia was not invited to the conference. It was the first arms control conference in history, and as Kaufman, 1990 shows, it is studied by political scientists as a model for a successful disarmament movement.
Held at Memorial Continental Hall in downtown Washington DC, it resulted in three major treaties: Four-Power Treaty, Five-Power Treaty (more commonly known as the Washington Naval Treaty), the Nine-Power Treaty, and a number of smaller agreements. These treaties preserved peace during the 1920s but were not renewed in the increasingly hostile world of the Great Depression.
The world's popular mood was peace and disarmament throughout the 1920s. Women had just won the right to vote in many countries, and they helped convince politicians that money could be saved, votes won, and future wars avoided by stopping the arms race. Across the world, leaders of the women's suffrage movement formed international organizations such as the International Council of Women and the International Woman Suffrage Alliance. Historian Martin Pugh says they achieved the greatest influence in the 1920s "when they helped to promote women's contribution to the anti-war movement throughout the Western world." In the United States, practically all the major Protestant denominations and highly visible Protestant spokesmen were strong supporters of international peace efforts. They collaborated with each other and worked to educate their local congregations on the need for peace and disarmament. 
At the end of World War I, Britain still had the largest navy afloat but its big ships were becoming obsolete, and the Americans and Japanese were rapidly building expensive new warships. Britain and Japan were allies in a treaty that was due to expire in 1922. Although there were no immediate dangers, observers increasingly pointed to the American-Japanese rivalry for control of the Pacific Ocean as a long-term threat to world peace. By this time, the British realized they had better cast their lot with Washington rather than Tokyo. To stop a needless, expensive and possibly dangerous arms race, the major countries signed a series of naval disarmament agreements.
The American delegation, led by Secretary of State Charles Evans Hughes, included Elihu Root, Henry Cabot Lodge and Oscar Underwood, the Democratic minority leader in the Senate. The primary objective of the conference was to restrain Japanese naval expansion in the waters of the west Pacific, especially with regard to fortifications on strategically valuable islands. Their secondary objectives were intended to ultimately limit Japanese expansion, but also to alleviate concerns over possible antagonism with the British. They were: first, to eliminate Anglo-American tension by abrogating the Anglo-Japanese alliance; second, to agree upon a favorable naval ratio vis-à-vis Japan; and, third, to have the Japanese officially accept a continuation of the Open Door Policy in China.
The British, however, took a more cautious and tempered approach. Indeed, British officials brought certain general desires to the conference--to achieve peace and stability in the western Pacific, avoid a naval arms race with the United States, thwart Japanese encroachment into areas under their influence, and preserve the security of Singapore, Hong Kong, and Dominion countries--but they did not enter the conference with a specific laundry list of demands; rather, they brought with them a vague vision of what the western Pacific should look like after an agreement.
Japanese officials were more focused on specifics than the British, and approached the conference with two primary goals: first, to sign a naval treaty with Britain and the United States, and, secondly, to obtain official recognition of Japan's special interests in Manchuria and Mongolia. Japanese officials also brought other issues to the conference--a strong demand that they remain in control of Yap, Siberia, and Tsingtao, as well as more general concerns about the growing presence of American fleets in the Pacific.
The American hand was strengthened by the interception and decryption of secret instructions from the Japanese government to its delegation. The message revealed the lowest naval ratio that would be acceptable to Tokyo; U.S. negotiators used this knowledge to push the Japanese to it. This success, one of the first in the U.S. government's budding eavesdropping and cryptology efforts, led eventually to the growth of such agencies.
The Washington Conference was called by President Warren G. Harding and run by Secretary of State Charles Evans Hughes. Harding demanded action in order to gain domestic political credit. Hughes--helped by the cryptographers who were reading the Japanese diplomatic secrets--brilliantly engineered a deal that everyone thought best for themselves. To resolve technical disputes about the quality of warships, the conferees adopted a quantitative standard, based on tonnage displacement (a simple measure of the size of a ship). A ten-year agreement fixed the ratio of battleships at 5:5:3--that is 525,000 tons for the USA, 525,000 tons for Britain, and 315,000 tons for Japan. Smaller limits with a ratio of 1.67 applied to France and Italy. Battleships, the dominant weapons systems of the era, could be no larger than 35,000 tons. The major powers allowed themselves 135,000:135,000:81,000 tons for the newly developed aircraft carriers.
The Washington Conference exactly captured the worldwide popular demand for peace and disarmament; without it, the US, Britain and Japan would have engaged in an expensive buildup, with each worried the other two might be getting too powerful. However, even with the restrictions, the agreement nonetheless solidified Japan's position as a great power as they got parity in the Pacific with the two leading global navies, were allowed to maintain a larger naval force than France and Italy, and were treated as a colonial power with equal diplomatic interests-a first for a non-Western nation. The agreements forced the US to scrap 15 old battleships and 2 new ones, along with 13 ships under construction.
The naval treaty was concluded on February 6, 1922. Ratifications of that treaty were exchanged in Washington on August 17, 1923, and it was registered in League of Nations Treaty Series on April 16, 1924. Japan agreed to revert Shandong to Chinese control by an agreement concluded on February 4, 1922. Ratifications of that agreement were exchanged in Beijing on June 2, 1922, and it was registered in League of Nations Treaty Series on July 7, 1922.
The Washington Naval Treaty led to an effective end to building new battleship fleets and those few ships that were built were limited in size and armament. Numbers of existing capital ships were scrapped. Some ships under construction were turned into aircraft carriers instead.
Even with the Washington Treaty, the major navies remained suspicious of each other, and for a brief while (1927-30) engaged in a race to build heavy cruisers which had been limited to size (10,000 tons) but not numbers. That oversight was resolved on value of cruisers by the London Naval Treaty of 1930, which specified a 10:10:7 ratio for cruisers and destroyers. For the first time, submarines were also limited, with Japan given parity with the US and Britain at 53,000 tons each. (Submarines typically displaced 1,000-2,000 tons each.) The U.S. Navy maintained an active building program that replaced obsolescent warships with technically more sophisticated new models in part because its construction yards were important sources of political patronage, and well protected by Congress. During the New Deal, furthermore, relief funds were used to build warships. "The naval program was wholly mine," President Roosevelt boasted.
The pacts and treaties that resulted from the Washington Naval Treaty remained in effect for fourteen years until Japan ended participation in 1936.