In 1865, the federal government abolished almost all forms of slavery, but the 13th Amendment allowed for one exception: When the opportunity of servitude was punishment for a crime.
Sixteen state constitutions have similar language, but on Tuesday voters in Colorado elected to change the language of their state's constitution and abolish all forms of slavery.
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Article II, Section 26 of Colorado's constitution reads that there "shall never be in this state either slavery or involuntary servitude, except as a punishment for crime, whereof the party shall have been duly convicted." (Emphasis added)
In the future, because of Amendment A, it will read "There shall never be in this state either slavery or involuntary servitude." (Again, emphasis added.)
Not all the votes have been counted, but the amendment had 65% of the vote with more than four-fifths of precincts reporting as of Wednesday, according to the Colorado Secretary of State's Office.
"The margin is such that there is no doubt," said Lynn Bartels, a spokeswoman for the Colorado Secretary of State's Office.
Voters almost passed the amendment two years ago, but the wording was so unclear that it confused many people about whether they were voting for or against slavery, Jumoke Emery with Abolish Slavery Colorado has said.
"It's official! Amendment A passes!" the organization said on Facebook. "We couldn't have done it without your support. To all those who donated, volunteered, sent emails, shared Abolish Slavery Colorado's posts, and encouraged their friends and family to vote YES on Amendment A, we are most grateful."
Joe Salazar, a state representative who wrote the bill that became the amendment, said he was feeling "absolutely wonderful."
"Colorado is leading the way on so many progressive issues, including removing slavery from the constitution, I'm excited for what we do next," he said.