Nine-Power Treaty

The Nine-Power Treaty (Kyūkakoku Jōyaku (Japanese: 九カ国条約)) or Nine-Power Agreement (Chinese: 九國公約; pinyin: jiǔ guó gōngyuē) was a 1922 treaty affirming the sovereignty and territorial integrity of the Republic of China as per the Open Door Policy.

United States Secretary of State John Hay had issued the "Open Door Notes" of September–November 1899, followed by a diplomatic circular in July 1900, asking that all of the major world powers with vested interests in Qing-dynasty China declare formally that they would maintain an 'open door' to allow all nations equal rights and equal access to the treaty ports within their spheres of influence in China.

Fearing that the European powers and Japan were preparing to carve China up into colonies, Hay also added provisions that Chinese territorial and administrative integrity should be maintained.

During the Washington Naval Conference of 1921–1922, the United States government again raised the Open Door Policy as an international issue, and had all of the attendees (United States, Republic of China, Imperial Japan, France, Great Britain, Italy, Belgium, Netherlands, and Portugal) sign the Nine-Power Treaty which intended to make the Open Door Policy international law.

The Nine-Power Treaty lacked any enforcement regulations, and when violated by Japan during its invasion of Manchuria in 1931 and creation of Manchukuo, the United States could do little more than issue protests and impose economic sanctions.