The Civil war was the largest, most destructive conflict in the history of the United States. A total of 625,000 men died—more than in all previous American wars combined. The country changed in fundamental ways. The institutions of plantation society and the slave system crumbled in a cataclysm that uprooted centuries-old traditions and forged the framework of modern America. Mark Twain called it “a great conflagration which uprooted and discarded institutions that had been growing for generations, and which changed the political and social structure of a nation without precedent in history.”

The war started with a clash of interests and ideologies. Many white Northerners came to believe that slavery was a moral wrong and an economic disaster. They wanted a federal government that would prohibit slavery and protect free labor. Southerners, more confident that Lincoln would be forced to act against the institution, feared that any effort to limit it would destroy their region’s economy and send enslaved people to a fate worse than death.

Neither side was prepared for the scope of the conflict. Both governments began with large standing armies—the Union put up to 2.1 million military-age white men in uniform, and the Confederacy mustered between 800,000 and 900,000 (fragmentary records do not permit a precise count).

The national governments expanded their powers in an effort to sustain a sustained war effort. Both the Union and the Confederacy imposed national taxes, limited civil liberties, and used conscription. A national debt accumulated, and inflation drove prices up dramatically.