A label for Northerners who opposed the war and occasionally worked to undermine the war effort.

Copperheads were mostly northern Democrats who opposed all measures in support of war against the Confederacy. They wanted a negotiated peace. Republicans also applied the term copperhead to those suspected of aiding the Confederate cause during the Civil War.

The Copperheads were a faction of Democrats in the North who opposed the American Civil War, wanting an immediate peace settlement with the Confederates. The name Copperheads was given to them by their opponents the Republicans, probably derived from the venomous snake (the American copperhead) that strikes without warning — Copperheads reinterpreted this insult as a term of honor, and wore copper liberty-head coins as badges. They were also called "Peace Democrats" and "Butternuts".