Ft Sumpter and Pearl Harbor

The Allies' oil embargo against Japan had Japan down to less than a year's oil reserves. It was either knuckle under to the Allies or take the initiative.

In the same way, big business in the majority population northern states passed commercial laws to force the southern states to sell their cotton to the New England mills. The white southerners would have become commercial serfs to the northern industrialists. Follow the money!