at the age of 25, garrison joined the anti-slavery movement, later crediting the 1826 book of presbyterian reverend john rankin, "letters on slavery", for attracting him to the cause. for a brief time he became associated with the american colonization society, an organization that promoted the "resettlement" of free blacks to a territory (now known as liberia) on the west coast of africa. although some members of the society encouraged granting freedom to slaves, others considered relocation a means to reduce the number of already free blacks in the united states. southern members thought reducing the threat of free blacks in society would help preserve the institution of slavery. by late 1829–1830, "garrison rejected colonization, publicly apologized for his error, and then, as was typical of him, he censured all who were committed to it."