The North couldn’t produce cotton as cheaply as the South for northern mills. First the North taxed arriving southern cotton, but that was ruled unconstitutional. Then the North banned southern cotton.
The South reacted by selling to British mills. Then Britain sold the cheap material and clothing in the North. So the North blockaded southern shipping ports. That’s when it hit the fan.
What tax did the Federal Government impose on cotton being shipped to New England? What Legislation, passed by the U.S. Congress, banned Southern cotton? When, before April 1861, did the U.S. Navy blockade Southern shipping ports.