What league was Mark Twain a vice president of?

Mark Twain was a vice president of the American Anti-Imperialist League. He became one of the best-known literary figures associated with the organization, which opposed American expansion and especially the annexation of the Philippines.

The league was formed in 1898 during the Spanish-American War and argued that colonial rule violated the principle of government by the consent of the governed. Its leadership included prominent politicians, industrialists, labor leaders, and writers. The vice-presidential position was largely honorary, but the names attached to it gave the movement public credibility.

Twain's anti-imperialist views became especially forceful after 1899. In essays such as “To the Person Sitting in Darkness,” published in 1901, he used satire to criticize American conduct in the Philippines and China. He served as a vice president from 1901 until his death in 1910.

A related source of confusion is the Anti-Imperialist League of New York, whose vice-presidential roster also included Twain. The broader American Anti-Imperialist League is the standard answer to this question; the New York organization was a prominent affiliated branch.