slavery was not the dominating issue.. remember the vast majority of whites in the south did not own a slave.. slavery was a non issue based on the fact that slavery was legal in the united states at the outbreak of the civil war and legal during the war as well.. the proclamation given in '63 did not outlaw slavery.. it outlawed slavery in the seceded states.. not the border states at all.. it was a gimmick to let the federal soldiers (union) take the slaves away so that the south would be unable to use them to build roads , forts ect.. but in union held territories (border states like missouri, kentucky ect) the slaves were still used to build for the union.. a tad bit of hypocrisy to say the least..
we must also remember that lincoln himself stated to douglas that he would let the south have their slaves if it would restore the union.. he said this as late as 1864.. a year after the emancipation proclamation.. so as you can see it was not a big factor in the war.. lincoln tried to discuss a re union of the states in '64 and among the agreements was the south keeping the slaves..
now that being said.. why did the war break out? well.. say you are the south and the largest industry at the time was cotton and this staple is making washington rich.. the south was smart enough to figure out that they held the countries economy in their hands.. why give the profits to washington and the north? the north knew this also.. they also knew that the slaves were bringing in the crops.. so why would they illegalize it?.. they wouldnt..not in the areas with cotton anyway.. so teh south broke away.. (now because of the war the north became a industrial powerhouse and cotton became less of a factor)
so why did the north take on the anti slavery issue.. well.. many dont know this and it is not well documented in our history.. but england was a staunch supporter of the confederacy.. the supplied weapons and clothing for much of the war.. the south, when it saw its fortunes failing, turned to england for military support.. they wanted the blockade killed in the waters around the coast.. england was more than happy to do so since it also wanted a stake in the south and the cotton it held.. one of the obstacles that england had was its anti slavery government.. so deals were made to outlaw slavery in teh south over the next 10 or so years.. they were already granting freedom to those who would fight in 1865 (albeit a bit late).. and the south agreed to get rid of slavery to gain its independence.. we have to remember that slavery was not officially made illegal until years after the war.. the north knew that england would not aid the south because of its slavery stance and the norths (anti) slavery stance.. many also dont know that numerous regiments in the north mutinied when lincoln signed the proclamation stating that they would not fight for or against slavery..
so we have to remember what we do with all wars.. we try and make them sound nobel.. but if ya look real close the only thing that is at issue usually has to do with money and the economy..