Main activist arm of the U.S. abolition movement, which sought an immediate end to slavery in the country (see abolitionism ).
Cofounded in 1833 by William Lloyd Garrison and Arthur Tappan , it promoted the formation of state and local auxiliaries to agitate for abolition. Despite violent opposition, by 1840 the group had 2,000 auxiliaries and more than 150,000 members, including Theodore Weld and Wendell Phillips . Its most effective public meetings featured testimony by former slaves, including Frederick Douglass and William Wells Brown . In 1839 it split into two factions: a radical group led by Garrison that denounced the Constitution as supportive of slavery and a moderate faction led by Tappan that led to the birth of the Liberty Party .