Tarriff's were at a historic low before Ft.Sumter was fired on. Post ACW US Tarriff's increased and do did cotton exports from the American South I can later link you up with a chart on that. Nobody is going to go to war over tarriff's we don't have letters or diaries to that effect. If an argument is made that tarriff's actually was the main cause of the ACW then it would be helpful to know which products were worth dying for.There is a significant difference between revenue and protective tariffs. Revenue tariffs were used to generate revenue for the federal government but did not appreciably increase the cost of imported goods to the consumer. Protective tariffs, on the other hand, were designed to raise the price of foreign goods in order to encourage the purchase of comparable domestic products. High protective tariffs tend to support domestic production but they also hurt trade and were opposed by those in the import-export business. Since high protective tariffs were often reciprocated by other nations, high tariffs tended to stifle trade in general.
You asked what imported items were so critical to the Confederacy but that really isn’t the point. The very nature of the southern economy was what really mattered. The southern states depended on foreign trade to sustain their economy. They depended on the importation of goods from overseas because they had a small manufacturing base. Furthermore, the southern economy was very dependent on the export of their agricultural goods to other nations. Therefore, the south opposed any type of trade barriers such as protective tariffs which stifled foreign trade. High protective tariffs imposed an undue burden on import-export dependent regions such as the southern states. The southern states were opposed to protectionist tariffs because of the negative affect it had on their economy.