The civil war was fought over secession.
Partly correct. In the course of history, wars had historically been fought by two armies battling over land. The Civil War was more than this. It was the first war of ideas. It was a war of two civilizations, not merely two armies.
The Secession was brought on by the north's interference in the slave trade and ownership.
Partly correct, once again. This is a highly simplified version. The injection of slavery into the political arena (end of Gag Rule in 1846, KS-NB Act, Lecompton, Bleeding Kansas, etc...) is one reason. Another is the sharp mistrust of government despite what I believe were the good intentions of well meaning figures like James Buchanan, in part due to Bleeding Kansas and the Lecompton Constitution.
In addition, the South
believed it could survive on its own ("Cotton is King") financially in light of the panic of 1857 which nearly crippled the North and left most of the South unscathed.
And lastly, the South felt as though it had been politically ostracized from the republic following Lincoln's victory in 1860. Many of the Southern states didn't even have Lincoln on the ballot and he still won.
So from a Southern perspective, they saw it as the Northern elite assaulting their society's ideology itself, they believed they could survive on their own financially, and they felt politically cut off. This is essentially my thesis on the causes of the Civil War. Ideological. Economic. Political.
Not just "they fought over slavery".
"My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it." -- Abraham Lincoln