If someone claimed that the Cherokee nation was moved off their land and placed on a reservation, in order to free the slaves, it would seem to make it a noble cause but it would not make the assertion true. Freeing the slaves was not an official goal of the north until the emancipation proclamation; 20 months after the onset of war. Abraham Lincoln was personally opposed to slavery but officially he expressed a strong desire to maintain the union as it was. I don’t know how much clearer he could be, as he was in his letter to Horace Greeley, as I have cited earlier.
And I never said it was. But in your original post you questioned the claim that the war was about slavery. I'm merely pointing out that from the Union perspective it was not about slavery and never was about slavery. But from the confederate perspective it certainly was.