The holiday Juneteenth, celebrated on June 19th, commemorates that emancipation of slaves in the United States. The emancipation began on June 19th, 1865. Happy Juneteenth!
Correction: "*the* emancipation of *some* slaves" Juneteenth commemorates the enforcement of the Emancipation Proclamation in the State of Texas, which at that point was the last vestige of the Confederate States of America. The slaves owned and held in slave States which did not secede from the United States of America were not emancipated until December 6th/18th, 1865 with the ratification of the Thirteenth Amendment to the Constitution of the United States of America. Also, if you're going to say when emancipation "began," you should start with the Emancipation Proclamation or States abolishing slavery or the slave trade clause in the Constitution of the United States of America.