First and Second World Wars. Korean War. Russian Civil War. Viet Nam War. Cambodian Civil War. First, Second, and Third Indian-Pakistani Wars. War of the Roses. Shall I continue?
Because they couldn't get a decent price for their goods without shelling out to the North (who depended on slave labor, too!)? Because profit margins were so low that they had to have huge operations or run at subsistance levels?
No and no. Plantation agriculture was very profitable for the southern aristocracy. Their profit margins in the 10 years leading up to the war had never been higher.
Manumission was gaining ground in the South, it is far cheaper to hire someone and let them fend for themselves than to be the owner and have to provide housing, clothing, food, medical care, etc.
I would be interested in seeing what evidence you have to support this. Something from the leaders of the times would be nice.
As economics includes the natural resource bases to which a government may avail itself, including those occupied or conquered, it is inherently obvious that your understanding of history is on par with your understanding of economics. Any war over territorial dominion is a war involving economics.
Books have been written on the topic, but I suggest you avail yourself of an encyclopedia and look up the causes of those wars. I will not write volumes here in rebuttal to indicate the obvious.
Their profit margins in the 10 years leading up to the war had never been higher.
Again, economics apply. If your profit is higher (by expanding the size of your operation, like the vanishing independant farmers of today are being absorbed by larger operations), then there is in one sort of reckoning, only an increase in the amount of money the government is taking from you if you cannot effectively trade with whom you wish without punitive tarrifs.
As an analogy, if you make $20,000 per year, your income tax (bottom line, how much paid)is a relative pittance to the person who makes $100,000 per year.
If that tax is percieved as being unbalanced on a regional basis, if Californians paid Federal income tax at twice the rate New Yorkers did, y'all would have your dander up, too.
The leaders of the times were not hell-bent on freeing slaves, with the exception of a few Abolitionists. Especially Northern leaders who would see a rapid diminuition in taxable trade as farm econcmies collapsed. The slaves were the labor which harvested profitable, but labor-intensive crops. Some, such as tobacco, still have no effective mechanical means of being worked or harvested.
For Southern leaders to advocate forced manumission would have been tantamount to to the Iowa Governor advocating a tractor ban in Iowa.
So don't expect to see comments from the political leaders of the times.
However, when one does the simple arithmetic on how much it costs to feed, clothe, house, and provide health care for an employee 24/7/365 versus paying a wage and letting the employee fend for themselves, the equation works out toward manumission. Contrary to tedious Northern stereotypes of Southerners, then and now, simple arithmetic was not beyond even the 'aristocracy'. Manumission was on the rise. I suggest you do further research into how many slaves were owned, including those owned by free blacks.
I heartily reccommend sources published prior to the revisions of the 1930's, and especially prior to the 1960's, whence much has been obfusticated by political agendae, especially those of the NAACP and the Reparationists.