During the Civil War, President Abraham Lincoln struggled to preserve the American constitutional republic and Union that ensured liberty and equality for all Americans. To that end, Lincoln brought the country to fight fought to preserve the Union against the secession of the South at his election in 1860. Lincoln also fought to end the moral disgrace of slavery and issued the Emancipation Proclamation during the war in 1863 as a war measure based upon his presidential war powers to weaken the South. At the end of the war, several amendments to the Constitution were ratified to advance the natural and civil rights republic of the Declaration of Independence and Constitution for African-Americans.

The interests of northern and southern states grew increasingly divergent. Eleven states eventually seceded from the Union and formed the Confederate States of America. After the Civil War, Congress required that the southern states would approve the Thirteenth, Fourteenth, and Fifteenth amendments as a condition of their re-entry into the union. The 13th Amendment banned slavery throughout the United States. The Fourteenth Amendment granted citizenship to formerly enslaved people and banned states from passing laws that denied the privileges and immunities of citizens, due process, or equal protection of the law. The Fifteenth Amendment extended the right to vote to black men. The Fourteenth Amendment in particular was a dramatic departure from the Founders ’Constitution, and set the stage for dramatic increases in the size, scope, and power of the national government decades later.