Lincoln's relationship with slavery "evolved" during the war. In 1860 the Republican party platform promised that they were only opposed to the expansion of slavery, they did not propose to end it. In the early stages of the war Lincoln reiterated his modest goals with respect to slavery in order to try to keep slave states in the union (this partially worked) and to broker a quick end to the rebellion.
With the Emancipation Proclamation Lincoln made his cause explicitly anti-slavery, and in the 1864 election the Republican platform explicitly included the complete abolition of slavery.
For the rebels, the preservation of slavery was always the primary cause for the rebellion. The fact that a Republican could become president -- even one on a limited platform -- was proof enough to them that slavery was not safe from political reform as long as they remained in the union.
For a brilliant account of the relationship between slavery and rebellion I recommend The Fall of the House of Dixie by Bruce Levine:
With the Emancipation Proclamation Lincoln made his cause explicitly anti-slavery, and in the 1864 election the Republican platform explicitly included the complete abolition of slavery.
For the rebels, the preservation of slavery was always the primary cause for the rebellion. The fact that a Republican could become president -- even one on a limited platform -- was proof enough to them that slavery was not safe from political reform as long as they remained in the union.
For a brilliant account of the relationship between slavery and rebellion I recommend The Fall of the House of Dixie by Bruce Levine:
http://www.amazon.com/Fall-House-Dixie-Revolution-Transforme...