I’m convinced it was reason #2. Listing the Northern states’ violation of the Constitution was a pretext. It provided them a legal excuse to do what the wanted to do anyway - become independent, set their own trade policies and stop sending so much money North in tribute to others.
With lower tariffs, the British and French could afford more of their cash crops and they would also pay lower prices for manufactured goods than they were paying. They would also not see the additional money from those tariffs paying for infrastructure projects and corporate subsidies for others as had been the case up to 1860.
The vast majority of all wars in human history have been about money. Governments almost never admit that’s what they are fighting for but in the end its obvious they are. It was no different here. Plenty saw it.
” If it be not slavery, where lies the partition of the interests that has led at last to actual separation of the Southern from the Northern States? …Every year, for some years back, this or that Southern state had declared that it would submit to this extortion only while it had not the strength for resistance. With the election of Lincoln and an exclusive Northern party taking over the federal government, the time for withdrawal had arrived … The conflict is between semi-independent communities [in which] every feeling and interest [in the South] calls for political partition, and every pocket interest [in the North] calls for union. So the case stands, and under all the passion of the parties and the cries of battle lie the two chief moving causes of the struggle. Union means so many millions a year lost to the South; secession means the loss of the same millions to the North. The love of money is the root of this as of many other evils … the quarrel between North and South is, as it stands, solely a fiscal quarrel.” – Charles Dickens
Charles Dickens nailed it.