War motives? In my mind, the North initiated the use of force with the South.
The Southern states wanted to freely trade with industrialized England (supply cotton for their established industrial machinery). Lincoln probably was worried about the South getting too cozy with England so soon after the previous war of independence! He also needed to help (return favor to) his industrial buddies, railroad and banker friends in the North (He wanted to collect tax/tariff/regulate the South so that it could not freely choose overseas competition when selling their raw materials, cotton in particular.)
The shallow draft steamboat design suddenly allowed full use of the Mississippi River and allowed the South to float away from railroad dependence and also sail off to find new raw cotton customers other than just the newly industrializing North.
The South tried to part ways peacefully over these issues, but the North (federal) was obsessed with control, regulation, tax, tariff, and free trade interference.
The line in the sand was crossed when the South said, “We won’t be forced to support you and we don’t need you, so F’off already!”
That kind of secession talk really sets tyrants off, like poking a bee hive with a stick. To Lincoln and his buddies, the South looked like a whole bunch of escaping slaves the needed to be re-captured, contained and taught a lesson!
How soon we forget.
Today, I see no reason to doubt this kind of treason won’t eventually give the ‘ole tree of liberty a good waterin' again.