Following the end of the Civil War in 1865, Congress passed three amendments to the Constitution. Collectively known as the "Reconstruction Amendments," the Thirteenth, Fourteenth, and Fifteenth Amendments together abolished chattel slavery and guaranteed full citizenship and voting rights to African Americans across the United States. It took more than 230 years for all states to ratify the Reconstruction Amendments. 

In 1863, Lincoln’s Emancipation Proclamation declared, "all persons held as slaves within any State, or designated part of a State, the people whereof shall then be in rebellion against the United States, shall be then, thenceforward, and forever free." Thus, enslaved people in Confederate states were freed by the Emancipation Proclamation. But because the border states of Maryland, Delaware, Missouri, and Kentucky, as well as areas retaken by Union were not actively "in rebellion" against the United States at the time of the Emancipation Proclamation, it did not apply to these areas. Additional legislation was needed to legally end chattel slavery in the United States. 

The Thirteenth Amendment, ratified in December 1865, ended chattel slavery and involuntary servitude throughout the United States.

Months later, Congress passed the nation's first civil rights bill -- the Civil Rights Act of 1866 -- in response to the black codes passed by many states limiting the rights of African Americans. Following the Civil Rights Act of 1866, the Fourteenth and Fifteenth Amendments solidified the civil rights of African Americans as constitutional law. 

The Fourteenth Amendment, ratified in July of 1868, guaranteed full citizenship to African Americans. The Fourteenth Amendment also placed restrictions on former Confederate leaders, wiped out all debts taken on by seceded states and the Confederate government, ensured that no former enslaver could be compensated for the loss of his "slave property," and defined national citizenship for the first time. 

The Fifteenth Amendment, officially ratified in March 1870, prohibited the denial of voting rights based on "race, color, or previous condition of servitude."

All former Confederate states were required to ratify the Thirteenth and Fourteenth Amendments before they could be readmitted to the Union. Any state that had not been readmitted before Congress passed the Fifteenth Amendment were required to ratify that as well.

Three former slave states rejected ratification of the Fifteenth Amendment: Kentucky, Delaware, and Tennessee. Kentucky and Delaware, which had never seceded, and Tennessee, which had already been readmitted to the Union in 1866, rejected ratification of the Fifteenth Amendment for more than a century. Delaware ratified the Fifteenth Amendment in 1901, followed by Kentucky in 1962. Tennessee was the last state to ratify the Fifteenth Amendment when it did so in 1997.

Amendment XIII

Section 1.

Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.

Section 2.

Congress shall have power to enforce this article by appropriate legislation.

Amendment XIV

Section 1.

All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside. No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.

Section 2.

Representatives shall be apportioned among the several states according to their respective numbers, counting the whole number of persons in each stateEach state receives seats in the House of Representatives based on its population. Before the Civil War, slaves were counted as three-fifths of a person for the purpose of determining a state’s population and representation in Congress. This clause of the Fourteenth Amendment ended that practice. (With slavery already eliminated by the Thirteenth Amendment, this clause may not have been necessary.), excluding Indians not taxed. But when the right to vote at any election for the choice of electors for President and Vice President of the United States, Representatives in Congress, the executive and judicial officers of a state, or the members of the legislature thereof, is denied to any of the male inhabitants of such state, being twenty-one years of age, and citizens of the United States, or in any way abridged, except for participation in rebellion, or other crime, the basis of representation therein shall be reduced in the proportion which the number of such male citizens shall bear to the whole number of male citizens twenty-one years of age in such stateThis clause punished states who disfranchised (took the vote from) African American men. If a state refused to allow any men over the age of 21 to vote, those men would not be counted in its population, and its representation in the U.S. House of Representatives would be reduced. The only reasons a person could be denied the right to vote is if he had supported the Confederacy and refused to take an oath of loyalty to the United States, or if he had committed a felony..

Section 3.

No person shall be a Senator or Representative in Congress, or elector of President and Vice President, or hold any office, civil or military, under the United States, or under any state, who, having previously taken an oath, as a member of Congress, or as an officer of the United States, or as a member of any state legislature, or as an executive or judicial officer of any state, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof. But Congress may by a vote of two-thirds of each House, remove such disability.

Section 4.

The validity of the public debt of the United States, authorized by law, including debts incurred for payment of pensions and bounties for services in suppressing insurrection or rebellion, shall not be questioned. But neither the United States nor any state shall assume or pay any debt or obligation incurred in aid of insurrection or rebellion against the United States, or any claim for the loss or emancipation of any slave; but all such debts, obligations and claims shall be held illegal and void.

Section 5.

The Congress shall have power to enforce, by appropriate legislation, the provisions of this article.

Amendment XV

Section 1.

The right of citizens of the United States to vote shall not be denied or abridged by the United States or by any state on account of race, color, or previous condition of servitude.

Section 2.

The Congress shall have power to enforce this article by appropriate legislation.