TheNine-Power Treaty (Kyūkakoku Jōyaku (Japanese:九カ国条約)) orNine-Power Agreement (Chinese:九國公約;pinyin:jiǔ guó gōngyuē) was a 1922 treaty affirming the sovereignty and territorial integrity of theRepublic of China as per theOpen Door Policy. The Nine-Power Treaty was signed on 6 February 1922 by all of the attendees to theWashington Naval Conference:Belgium,China,France, theUnited Kingdom,Italy,Japan,^[1] theNetherlands,Portugal,^[2] and theUnited States.

United States Secretary of StateJohn 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 inQing-dynasty China declare formally that they would maintain an 'open door' to allow all nations equal rights and equal access to thetreaty ports within theirspheres of influence in China. Fearing that theEuropean powers andJapan were preparing to carve China up into colonies, Hay also added provisions that Chinese territorial and administrative integrity should be maintained.

Although no nation specifically affirmed Hay’s proposal, Hay announced that each of the powers had granted consent in principle and treaties made after 1900 make reference to theOpen Door Policy. Nonetheless, competition between the various powers forspecial concessions within China, includingrailroad rights,mining rights,loans,treaty ports open to foreign trade, andextraterritorial privileges continued unabated.

The United States was especially leery of Japanese designs on China, after theRusso-Japanese War (1904–1905) and theTwenty-One Demands (1915) and repeatedly signed agreements with the Japanese government pledging to maintain a policy of equality inManchuria and the rest ofMainland China. These agreements concluded withLansing–Ishii Agreement in 1917, which was soon shown to be completely ineffective.

During theWashington Naval Conference of 1921–1922, the United States government again raised theOpen 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, andPortugal) sign the Nine-Power Treaty which intended to make the Open Door Policyinternational law.

The Nine-Power Treaty, concurrent with the Shantung Treaty of the Washington Naval Conference, effectively prompted Japan to return territorial control ofShandong province, of theShandong Problem, to the Republic of China.^[3] The Nine-Power Treaty was one of several treaties concluded at the Washington Naval Conference. Other major agreements included theFour-Power Treaty, theFive-Power Treaty, and the Shangtung Treaty.

The Nine-Power Treaty lacked any enforcement regulations, and when violated by Japan during itsinvasion of Manchuria in 1931 and creation ofManchukuo, the United States could do little more than issue protests and imposeeconomic sanctions. In November 1937, the signatories of the Nine-Power Treaty convened in Brussels for theNine Power Treaty Conference after the outbreak of theSecond Sino-Japanese War but to no avail. However, the treaty eventually had a role in checking Japanese aggression during the 1932Battle of Shanghai.^[4]

World War II effectively ended the Nine-Power Treaty.^{[citation needed]}

• Baer, George (1996).One Hundred Years of Sea Power: The U.S. Navy, 1890-1990. Stanford University Press.ISBN 0-8047-2794-5.
• Ellis, L. Ethan.Republican foreign policy, 1921-1933. Rutgers University Press, 1968. pp. 79–136.
• Fenwick, C. G. "The Nine Power Treaty and the Present Crisis in China".American Journal of International Law 31.4 (1937): 671-674.JSTOR 2190677.
• Lamb, Margaret (2001).From Versailles to Pearl Harbor: The Origins of the Second World War in Europe and Asia. Palgrave Macmillan.ISBN 0-333-73840-3.
• Myer, Carl L (1936).Treaty Relations Between the United States and the Far East (with Special Reference to the Four-Power, Five-Power, and Nine-Power Treaties). Library of Congress Legislative Reference Service.ASIN B0008D24WG.

• "Principles and Policies Concerning China (Nine-Power Treaty), Feb. 6, 1922, 44 Stat. 213, 2 U.S.T. 375"
• The full text of the Nine-Power Treaty

• Interwar-period treaties
• Treaties concluded in 1922
• Treaties of the Republic of China (1912–1949)
• Treaties of the United States
• Treaties of the Empire of Japan
• 1922 in China
• 1922 in Japan

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