This might shed some light on the North’s invasion of the CSA.
It wasn’t a Civil War. Never was. The victors write the history books.
A civil was is when opposing sides fight for control of the central government. The South wanted no part of the central government. The South wanted to secede and form its own government.
The North didn’t want the South to secede. So the North invaded the South.
And started the War Between the States — or, as we call it in the South, The War of Northern Aggression.
(No, for the public school educated, the war wasn’t fought over slavery either. It was a war of secession.)