What legal action during the civil war ended slavery in states that had left the union

The legal action that ended slavery in states that had left the Union during the Civil War was the Emancipation Proclamation.

Explanation:

The Emancipation Proclamation was a presidential proclamation and executive order made on September 22, 1862 by the President of the United States Abraham Lincoln, which entered into force on January 1, 1863, abolishing slavery throughout Confederate territory during the Civil War.

At the time of its ratification, the Proclamation freed a minimum number of slaves, but as the Union annexed the Confederate territories, it paved the way for the total abolition of slavery on America. Slavery became illegal through the approval of the 13th Constitutional Amendment, a fact that occurred in 1865.

The executive order was severely criticized in the southern states, whose economic activity was based on slave labor. However, adherence of this measure to all Confederate states ensured Lincoln's main focus: strengthening Union ties.

Answer: Lincoln issued the Emancipation Declaration or Proclamation 95 that was a presidential proclamation and executive order issued by United States President Abraham Lincoln effective January 1, 1863. It changed the legal status under federal law of more than 3.5 million enslaved African Americans in the Confederate states from slave to free. As soon as a slave escaped the control of the Confederate government, either by running away across Union lines or through the advance of federal troops, the slave was free. Ultimately, the Union victory brought the proclamation into effect in all of the former Confederacy. The remaining slaves, those in the areas not in revolt, were freed by state action, or by the Thirteenth Amendment to the United States Constitution, ratified in December 1865.