“If you look at the causes the originally propelled the Union and the Confederacy to warfare it was the United States army fighting to preserve the Union and the Confederate States army fighting to protect slavery. Read the words of Lincoln, read the words of the secessionists in their state declarations of causes.”
Stop getting your history from Hollywood.
” My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that.”
~Abe Lincoln August 22, 1862
That's exactly what I said. The US army fought to preserve the Union and Constitution, not to establish an all-powerful federal government.
But the Confederacy seceded to preserve slavery as Mississippi's declaration of secession stated:
"Our position is thoroughly identified with the institution of slavery - the greatest material interest of the world."
That's history, not Hollywood.