Follow the money.
"Blockade Southern Ports. If not a series of customs houses will be required on the vast inland border from the Atlantic to West Texas. Worse still, with no protective tariff, European goods will under price Northern goods in Southern markets. Cotton for Northern mills will be charged an export tax. This will cripple the clothing industries, and make British mils prosper. Finally,, the great inland waterways, the Mississippi, the Missouri, and the Ohio Rivers will be subject to Southern tolls.
A newspaper that supported Lincoln said: ( Philadelphia Press on March 18, 1861)
"One of the most important benefits which the Federal Government has conferred upon the nation is unrestricted trade between many prosperous States with divers productions and industrial pursuits. But now, since the Montgomery Congress has passed a new tariff, and duties are extracted on Northern goods sent to ports in the Cotton States, the traffic between the two sections will be materially reduced)
"Another, and a more serious difficulty arises out of our foreign commerce, and the different rates of duty established by the two tariffs which will soon be in force".
"The General Government,to prevent the serious diminution of its revenues, will be compelled to blockade the Southern ports and prevent the importation of foreign goods into them, or to put another expensive guard upon the frontiers to prevent smuggling into the United States.