The strong suggestion in this thread is that higher tariffs led to secession. That dog won't hunt. Higher (above 25%) tariffs had not been in force since the Walker Tariff of 1846. Plus, higher rates were not favored by everyone in the North, and different leaders in South spoke in favor of higher rates.

Higher rates were not enacted until Southern Congressmen left Washington in 1861 and the Morrill Tariff became law.