During the American Civil War (1861-1865), the Copperheads nominally favored the Union but strongly opposed the war, for which they blamed abolitionists, and they demanded immediate peace and resisted draft laws.
Some historians, such as Richard Curry, have downplayed the treasonable activities of the Copperheads, arguing that they were simply people who fiercely resisted modernization and wanted to return to the old ways.
The Copperheads did not avert the Civil War, nor can they be said to have totally repudiated violence.
The sentiments of Copperheads attracted Southerners who had settled north of the Ohio River, conservatives, the poor, and merchants who had lost profitable Southern trade.
The Copperheads advocated this principle at a time when some thought negotiation too risky an enterprise, too prone to compromise and accommodation, and wanted outright victory instead, which only war could deliver.
Copperheads distrusted monopolies and a strong central government, urging instead more power for the states.
The Copperheads had numerous important newspapers, but the editors never formed an alliance.
Some Copperheads tried to persuade Union soldiers to desert.
The New York Journal of Commerce, originally abolitionist, was sold to owners who became Copperheads, giving them an important voice in the largest city in the North.
The Copperheads would reach their lowest point following the Union Army's success in the Atlanta Campaign.
Copperheads did well in local and state elections in 1862, especially in New York, and won majorities in the legislatures of Illinois and Indiana.
Copperheads were most numerous in border areas, including southern parts of Ohio, Illinois, and Indiana (in Missouri, comparable groups were avowed Confederates).
The Copperheads did not survive, nor did they attract enough support to achieve their aim.
The Copperheads sometimes talked of violent resistance, and in some cases started to organize.