Why did american indians occupy alcatraz island in 1969?

American Indians occupied Alcatraz Island in 1969 as a show of protest against the United States's constant choice to overlook or misrecognize rights and responsibilities set by treaties between tribes and the US government. Additionally (and more importantly) it was a retaliation against the theft of tribal land by the federal government. Protesters believed that if the federal government could illicitly occupy tribal lands, tribal members could just the same occupy federal lands.

The Occupation of Alcatraz was led by the Indians of All Tribes (IAT) as a form of inter-tribal solidarity. It preceded the more famous occupation of Wounded Knee in South Dakota during the early 1970s. That protest was organized primarily by the American Indian Movement (AIM).