|Founded||September 15, 1900|
|Dissolved||July 30, 1940|
One-party system of the Imperial Rule Assistance Association
Chuo Shimbun (ja) 
|Political position||Centre-right to right-wing|
Founded on September 15, 1900, by Itō Hirobumi, the Seiyūkai was a pro-government alliance of bureaucrats and former members of the Kenseitō. The Seiyūkai was the most powerful political party in the Lower House of the Diet of Japan from 1900 to 1921, and it promoted big government and large-scale public spending. Though labeled "liberal" by its own members, it was generally conservative by modern definitions. It often opposed social reforms and it supported bureaucratic control and militarism for the purpose of winning votes. It viewed the Rikken Minseitō as its main rival.
The Seiyūkai came into power in October 1900 under the 4th Itō administration. Under its second leader, Saionji Kinmochi, it participated in the Movement to Protect Constitutional Government from 1912 to 1913. It was the ruling party under the Prime Minister Yamamoto Gonnohyōe from 1913 to 1914. Cabinet minister (and later 4th party president) Takahashi Korekiyo helped reinforce its ties with the zaibatsu, especially the Mitsui financial interests.
The 3rd party president, Hara Takashi, became Prime Minister in September 1918, and assigned every cabinet post except for the Army Minister, Navy Minister and Minister of Foreign Affairs to members of the Seiyūkai. In the 1920, the party reached the peak of its popularity.
After Hara's assassination in 1921, a large block of party members defected to form the Seiyūhontō in the 1924 General Election; however, the Seiyūkai retained enough seats to dominate the cabinet of its 5th party president, General Tanaka Giichi from 1927 to 1929.
While in the opposition during the Minseitō-dominated cabinet of Prime Minister Hamaguchi Osachi, the Seiyūkai attacked the ratification of the London Naval Treaty of 1930 as against Article 11 of the Meiji Constitution, which stipulated the independence of the military from civilian control.
After winning the 1932 General Election under Inukai Tsuyoshi, Seiyūkai formed a cabinet, floated the yen and conducted policies to revive the economy. However, after Inukai’s assassination in the May 15 Incident of 1932, factionism within the party limited its effectiveness.
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In 1900, Ito Hirobumi and Saionji Kimmochi collaborated with the conservative group to found the Rikken Seiyukai, Constitutional Association of Political Friends
- Steven Casey, Jonathan Wright, ed. (2008). Mental Maps in the Era of Two World Wars. Palgrave Macmillan. p. 116.
Ultimately , in the face of mounting pressures from the military hardliners and the conservative opposition party Rikken Seiyūkai ( Friends of Constitutional Government Party, ...
- Kent E. Calder, ed. (2021). Crisis and Compensation: Public Policy and Political Stability in Japan. Princeton University Press. p. 188. ISBN 9780691229478.
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- Urs Matthias Zachmann, ed. (2017). Asia after Versailles: Asian Perspectives on the Paris Peace Conference and the Interwar Order, 1919-33. Edinburgh University Press.
- The Linkage Between Domestic and International Conflict: The Case of Japanese Foreign Policy, 1890-1941. University of Michigan. 2004. p. 267.