[worik]

Lincoln wanted to save the union. He did not care about slaves (there was slavery in the north too, but the economy did not depend on it)

The South seceded because of the threat to slavery and the writing on the wall about the way that was going.

So, yes, the USA Civil War was about slavery. The fact that Lincoln did not fight "for the slaves" or even "free the slaves" (the slaves in the North were not freed by the Emancipation Declaration" but by the Thirteenth Amendment) is not relevant.

It is not "semantics", it is a simple fact.