Washington Conference

International diplomatic meeting 1921 to avert a naval arms race between the principal maritime powers – Britain, the USA, Japan, France, and Italy. China, the Netherlands, Portugal, and Belgium were also represented. The resultant treaty 1922 put a stop to naval competition by limiting the battleship strength of the five powers.

The conference was summoned by US president Warren Harding, and assembled in Washington, DC, on 11 November 1921. They reached an agreement signed 6 February 1922 to a tentative ten-year building ‘holiday’, limiting both the maximum individual tonnage of, and the maximum calibre of gun to be mounted in, capital ships, aircraft carriers, and cruisers respectively.

To satisfy Japan's desire for security, it was agreed that none of the powers should augment the defences of their outlying possessions in the Pacific. This meant that, while Japan was forbidded to fortify its mandated islands, the USA could not strengthen the Philippine bases or those of Guam. With this agreement concluded, the Anglo-Japanese alliance was allowed to lapse.

The treaty lasted until the London Naval Conference 1930.