Which amendment officially freed 4 million slaves after the Civil War?

The 13th Amendment officially abolished slavery in the United States, thereby freeing approximately four million enslaved individuals following the Civil War. Ratified in December 1865, this amendment marked a significant legal transformation in American society by prohibiting involuntary servitude, except as punishment for a crime. The amendment was a crucial part of the Reconstruction era, as it aimed to secure civil rights for formerly enslaved people and to reshape the socio-economic landscape of the South.

The other amendments mentioned serve different purposes. The 14th Amendment, ratified in 1868, focused on granting citizenship and equal protection under the law to all persons born or naturalized in the U.S., including former slaves. The 15th Amendment, ratified in 1870, aimed to protect voting rights regardless of race, color, or prior condition of servitude. The 16th Amendment, ratified in 1913, dealt with income tax, which is unrelated to the status of slavery or civil rights. Therefore, the 13th Amendment stands out as the critical legal measure that formally ended the institution of slavery in the United States.