Introductory comment

I Legislature
II Executive
III Judiciary
IV The States
V Amending
VI Miscellaneous
VII Ratification
Bill of Rights
Pre-Civil War
Post-Civil War
20th Century
The Constitution of the United States of America

Post-Civil War Amendments
Amendment XIII (1865)

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 (1868)

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 state, 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 state.
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.
  Sections 2 onwards are essentially mechanistic provisions tidying up some post-Civil War loose ends. Section 1 is however something else.
Even there the only problem is with the first clause of the second sentence: "No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States" and even there it only becomes the true danger it is when taken together with the ninth amendment.
Effectively the sentence kills States rights. It repeals the tenth amendment and in practice makes pointless the apparent limitations of power established by section 8 of article 1.
Without the ninth amendment, even this is not of itself a threat to a reasonable society: at what level of the political hierarchy certain questions are decided is to some extent a matter of taste.
What matters is not so much who makes decisions but when and how they are made and promulgated: and the ninth amendment says in short: "You cannot for certain know what your rights, immunities and privileges are until the Supreme Court has ruled (and it may rule differently next time". This amendment adds to that the rider: "And you cannot rely on your State courts or legislature to protect you or give you guidance".
Everything is now at the whim of an unelected, politically appointed, chamber.

Amendment XV (1870)

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.