That's a pretty piece of rhetoric, but while the South went to war to preserve slavery, the North went to war to preserve the Union. Yet slavery was the issue that drove the entire thing forward.
“That’s a pretty piece of rhetoric, but while the South went to war to preserve slavery, the North went to war to preserve the Union.”
Some say the North fought to preserve their ability to collect import taxes. Lincoln for example.
It wasn't about "preserving the Union." Lincoln was going to give up Ft. Sumter if Virginia would offer assurances that they would remain in the Union.
Lincoln was willing to accept the breakup of the Union provided it didn't get too big. He would have let the seven go in exchange for keeping Virginia.
Virginia was going to give him those assurances, but by the time they told him so, it was already too late. He had already sent the attack fleet against the Confederates in Charleston.