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Originally posted by Rodeo
This seems a balanced analysis:

Slavery proved unprofitable in the Northern states and by the early 19th cent. had disappeared. Its abolition had been hastened by the work of the Quakers, who, as in Great Britain, were staunchly opposed to the institution. In the South, however, where African slaves arrived in the tens of thousands from the late 17th through the early 18th cent., slavery came to be an integral part of the plantation system (especially after the introduction of the cotton gin in 1793). From the late 18th cent. to the eve of the Civil War, more than a million slaves were moved from the Eastern Seaboard to the Deep South, where many labored in the sugar and cotton fields. This vast internal slave trade, which often tore slave families apart, was the South's second largest enterprise; only the plantation system itself surpassed it in size.

In the Northern United States, humanitarian principles led to the appearance of the abolitionists. They knew little of the actual conditions in the South and were fighting not for economic reform but for idealistic principles. The abolitionists in general tended to regard slavery as an unmitigated evil. The small Northern farmer also feared slavery as a system of cheap labor against which it was difficult to compete.

The South, eager to conserve the status quo, developed a bellicose defense of the system, which was hardened by such factors as the slave uprising led by Nat Turner, the troubles over fugitive slaves, and the very active propaganda against the South. The question, involving the very existence of Southern society as then organized, was the dominant one in U.S. history from 1830 to 1860. The political expression of the struggle was largely an attempt on the part of the South to maintain legislative guarantees of the system against the efforts of the abolitionists.

The chief question concerned the right of extension of slavery in the Western territories. This first became important in 1820 with the Missouri Compromise. Many leading statesmen of the time sought an answer: Henry Clay, the great compromiser; Daniel Webster; John C. Calhoun; Stephen A. Douglas, who proposed popular sovereignty as means to decide the free or slave status of territories; and the uncompromising antislavery men, such as Charles Sumner and William H. Seward. The great compromises—the Missouri Compromise, the Compromise of 1850, and the Kansas-Nebraska Act—were ultimately ineffective.

Sectional opposition, which involved even broader questions than slavery, including the constitutional issue of states' rights, grew more passionate as the two sections became more and more hostile. The Ostend Manifesto and the proposed annexation of Cuba, the fugitive slave laws, the operations of the Underground Railroad, the furor caused by the Dred Scott Case, the Wilmot Proviso—all heightened the tension. Sporadic armed conflict erupted in Kansas and in the Harpers Ferry raid of John Brown. The struggle became more clearly defined as the Republican party was formed with a definite antislavery platform.

In the victory of the Republican presidential candidate, Abraham Lincoln (1860), the South saw a threat to Southern institutions, and the Southern states in an effort to secure those institutions resorted to secession and formed the Confederacy. The Civil War followed, and the victory of the North brought an end to slavery in the United States. Lincoln's Emancipation Proclamation (issued in 1863, it declared all slaves in the Southern secessionist states free) was followed by other legislation, especially the Thirteenth Amendment to the Constitution.

The end of the Civil War did not result in the integration of the former slaves into American life. Although there were gains toward this under Reconstruction, these were subsequently reversed by the Jim Crow laws. Generally easily identified by the color of their skin, African Americans were subjected to segregation and other forms of discrimination practiced by most white Americans and legislated in many jurisdictions. This situation did not begin to be ameliorated until the civil-rights struggles of the 20th cent. (see civil rights; integration).

The only problem with the above is that it's mostly unsupported by the historical facts.

Incidently, there were more abolitionist groups in the Confederate States than in the northern states, a lot more.

And, slavery was immensely successful in the north. Two major profit centers for slavery were Massachusetts and Rhode Island.