With the history of America's "Civil War" having recently reentered the political spotlight, it has become apparent just what precious little Americans know about their own country's history. Those who wish to truly understand the causes of the War between the States must first endeavor to understand the construction of the United States, that the United States were constituted as a Union of sovereign states. In this context, it is essential to understand that each state then reserved the right to secede from the Union, as articulated in the Declaration of Independence, throughout the Constitutional Conventions, and upon ratification of the Constitution.
One must also study the Constitution of the Confederate States of America, the addresses and the statements issued by Lincoln and his administration, the Corwin Amendment, the history of the American Colonization Society, the political and economic implications of the Morrill Tariff and westward expansion, the implications of a General Government becoming such a force within the states, and the events and circumstances surrounding the battle at Fort Sumter after the State of South Carolina had already declared its secession from the Union; after the State of South Carolina had already demanded that the Union Army vacate the fort; and after the State of South Carolina had already offered compensation to the Union in return.
Ultimately, the Union Army’s continued occupation of Fort Sumter, its Southern blockade, its imposition of onerous tariffs, and its incursion into the Southern States constituted treason as defined in Article III, Section 3, Clause 1 of the United States Constitution: "Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort." And, where the term "United States" appears within the Constitution, it is in the plural, regarding the States severally in their sovereign capacity as declared in the Declaration of Independence, as acknowledged in the Treaty of Paris, and as reaffirmed in the compacts which formed the Union.
Ultimately, at the very core of the matter we find this: Slavery was not the cause of the Civil War. It was, however, one of the political issues named among the States’ declared causes for secession. There is a difference. In fact, had the Civil War ended within two years after it officially began at Fort Sumter — or within the even shorter timeframe expected by Lincoln — nobody today would connect the war to slavery, specifically because it was a war waged by Lincoln to "preserve the Union" and, by that, to preserve the General Government’s major tax base in the South.
It was only several years into the war, after the issue of slavery became expedient to the cause of the Federals, that the Emancipation Proclamation was issued as a war measure to foment unrest in the South and to conscript slaves into the Union Army. To believe that the Civil War for both sides centered on the issue of slavery is to believe that the Allies’ efforts in World War II were inspired by the Holocaust or the plight of the Jews. That is to say that both beliefs are naive, unfounded in both reason and history.
For those interested in discovering the true history and the various events comprising this critically important part of American history, please read America's Founders on the Matter of States' Rights and America's Civil War: Not "Civil" and Not About Slavery.