The controversies over interposition, nullification (both involving claims that states could defy Federal laws), secession, and slavery that led to the Civil War were settled on the battlefield but confirmed later by amendments to the Constitution.

The Three Postwar Amendments

From 1865 to 1870, the states ratified three critical amendments. The first of these, the Thirteenth Amendment, abolished involuntary servitude in the United States except as a punishment for crimes. The Fourteenth Amendment, ratified in 1868, applied citizenship to all persons born and naturalized within the United States and guaranteed all such individuals certain fundamental rights, including equal protection under the law. The Fifteenth Amendment guaranteed that no citizen would be denied the right to vote on the basis of "race, color, or previous condition of servitude." Each of these amendments vested Congress with enforcement powers.

Conflict over slavery was a major factor in the...