While it’s important to remember that gold may make the rule, historians agree that slavery, at the time of the US Civil War/War of Northern Agression, was a major, practically a single-voting issue. A quick review of history bears this out:
1854 – Lincoln declared in his “Peoria Speech” his opposition to slavery. Prior to this, he had been on the fence, wanting to keep slavery out of the new territories to the west. He will vacillate on this position when politically expedient, but what’s clear is he opposes slavery.
1854 – Unable to obtain a majority in six rounds of voting, Lincoln withdraws from a Senate race and instructs his backers to vote for Lyman Trumball, an antislavery Democrat.
1856 – The Whig Party splits over the issue of slavery. Drawing from antislavery Democrats and the abolitionist Whigs, the Republican Party is formed. Lincoln is instrumental in this.
1856-1857 The Southern press reports that the newly formed Republican party only represents the anti-slavery advocates of the North, and not the whole Union. The Richmond Examiner specifically wrote: "[Republican] party founded on the single sentiment of hatred of African slavery."
1857 – Lincoln publicly denounces the Dred Scot decision, stating that it’s part of a conspiracy to support Slave Power.
1858 – Lincoln-Douglas Debates revolve on a single topic—slavery. Douglas wins re-election, but Lincoln gains recognition and a national platform.
1860 – Lincoln gives his “Cooper Union” speech in which he argues that the Founding Fathers sought to restrict slavery.
1860 – Lincoln begins presidential campaign as The Rail Candidate, and is depicted to be carried by the issue of slavery. He will win solely from votes in the West and the North. Not one Southern state will vote for Lincoln. Southern secessionist states make clear they will leave the Union before Lincoln takes office.
December 1860 – South Carolina adopts an “ordinance of secession”.
February 1861 – Six more states follow South Carolina. They declare themselves the Confederate States of America. In their articles of secession, four of the succeeding states specifically state slave-holder rights as the issue. Texas mentions slavery 21 times, and said, “[the Union was established] exclusively by the white race, for themselves and their posterity.”