The Civil War
The Civil War is the central event in America's historical consciousness. While the American Revolution created the United States，the Civil War of 1861-1865 determined what kind of nation it would be.
The war resolved two fundamental questions left unresolved by the revolution: whether the United States was to be a dissolvable confederation of sovereign states or an indivisible nation with a sovereign national government; and whether this nation, born of a declaration that all men were created with an equal right to liberty, would continue to exist as the largest slaveholding country in the world.
The Civil War started because of uncompromising differences between the free and slave states over the power of the national government to prohibit slavery in the territories that had not yet become states.
When Abraham Lincoln won election in 1860 as the first Republican president on a platform pledging to keep slavery out of the territories, seven slave states in the deep South seceded and formed a new nation, the Confederate States of America.
The incoming Lincoln administration and most of the Northern people refused to recognize the legitimacy of secession. They feared that it would discredit democracy and create a fatal precedent that would eventually fragment the no-longer United States into several small, squabbling countries.
Northern victory in the war preserved the United States as one nation and ended the institution of slavery that had divided the country from its beginning.
After the war, three important amendments were added on to the United States Constitution:
The 13th Amendment that prohibits slavery anywhere in the United States. This completed the work of the Emancipation Proclamation.
The 14th Amendment that guarantees that all people born in the United States are citizens with equal rights.
The 15th Amendment that guarantees that people in the United States cannot be kept from voting because of their race.
All these achievements came at the cost of 625,000 lives - nearly as many American soldiers as died in all the other wars in which this country has fought combined.