President Biden on Friday offered a "long overdue" formal apology from the government for the Federal Indian Boarding School Initiative, describing it as "one of the most horrific chapters in American history." 

The U.S. Department of the Interior says the program, which lasted over a 150-year period that ended in 1969, established 408 schools across 37 states to "culturally assimilate American Indian, Alaska Native and Native Hawaiian children by forcibly removing them from their families, communities, languages, religions and cultural beliefs." 

"After 150 years, the United States government eventually stopped the program. But the federal government has never, never formally apologized for what happened — until today," Biden told an audience while speaking at the Gila River Indian Community in Arizona. "I formally apologize, as President of the United States of America, for what we did. I formally apologize. That's long overdue." 

"At first, in the 1800s, the effort was voluntary, asking tribes... to send their children away to vocational schools. But then the federal government mandated the removal of children from their families and tribes, launching what's called the Federal Indian Boarding School era," he said. 

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President Biden speaks at the Gila Crossing Community School in Laveen, Arizona, on Friday. (AP/Rick Scuteri)

"One of the most horrific chapters in American history," Biden continued. "We should be ashamed, a chapter that most Americans don't know about." 

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Attendees clap at an event with President Biden at the Gila Crossing Community School on the Gila River Indian Community reservation in Laveen, Arizona, on Friday. (AP/Manuel Balce Ceneta)

"Generations of native children stolen, taken away to places they didn't know, with people they never met, who spoke a language they had never heard. Native communities silenced. Their children's laughter and play were gone," Biden also said. "Children would arrive at schools, their clothes taken off, their hair that they were told was sacred, was chopped off, their names literally erased, replaced by a number or an English name." 

President Biden said during his speech that the Federal Indian Boarding School era was one of the "most horrific chapters in American history." (AP/Manuel Balce Ceneta)

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At least 973 Native American children died during the program, during which more than 18,000 were taken from their parents, according to The Associated Press.