If, and I say if, Lincoln was fighting the war to “free the slaves” as the Gettysburg speech implied, he was fighting to overthrow the constitution of the United States.
The U.S. constitution enshrined slavery. Thirteen of the original 13 states had voted to make the U.S. constitution pro-slavery.
Absolute nonsense. Slavery was ended in the U.S. through Constitutional amendment, which is not an overthrow of the Constitution by any means. You'll have to do better than that to make your case.