[1] The Anti-Imperialist League was ultimately defeated in the battle of public opinion by a new wave of politicians who successfully advocated the virtues of American territorial expansion in the aftermath of the Spanish–American War and in the first years of the 20th century, although the organization lasted until 1920.

[6] Chosen as the high-profile President of the League was former Massachusetts Governor, Congressman, and United States Senator George S. Boutwell, who would remain in the position until his death in 1905.

In addition to its Boston-based governing center, the Anti-Imperialist League also included a large list of public figures of national reputation who were enlisted as Vice-Presidents of the organization.

[6] A total of 18 Vice-Presidents were named at the time of the November formation of the league, including among them former President of the United States Grover Cleveland, ex-US Senator and Secretary of the Interior Carl Schurz, industrialist Andrew Carnegie, and labor leader Samuel Gompers.

[7] Included among these were religious philosopher Felix Adler, former Iowa Governor William Larrabee, Republican Congressman Henry U. Johnson, and Stanford University president David Starr Jordan.

The group's largest and most influential local affiliates were located in New York City, Philadelphia, Washington, DC, Chicago, Minneapolis, Cincinnati, Portland, Oregon, and Los Angeles.

[14] Mark Twain, perhaps the most prominent member of the league, offered his voice through the publication of his essay "To the Person Sitting in Darkness," which appeared in the North American Review in February 1901.

In his essay, Twain satirically portrayed the moral and cultural superiority of Americans compared to Filipinos to comment on what he believed to be the great irony of the Philippines' annexation.

"[15] The Anti-Imperialist League of New York was particularly prominent in the production of propaganda pamphlets, drawing upon the impressive array of writers, public intellectuals, and politicians among its members.

Particularly controversial was the League's endorsement of William Jennings Bryan, a renowned anti-imperialist but also the leading critic of the gold standard, a position which alienated a substantial segment of the organization's leaders.

Following the death of George Boutwell in 1905, prominent lawyer and civil rights activist Moorfield Storey would serve as President of the organization, filling that role from 1905 until the League dissolved in 1920.