And even then it wasn't because they cared about the slaves, it was because they wanted revenge against the South for having fought them so hard.
It was because the South started the war, so their only option was to fight or surrender.
That the South started the War is one of the topics in dispute, but saying it's true for the sake of argument, your statement implies they abolished slavery "because the South started the war."
That is factually contradicted by both Abraham Lincoln and W.T. Sherman who make it clear that the South could have kept slavery, even though they are regarded by both parties as having "started the war."
In other words, you statement doesn't make logical sense. They obviously didn't abolish slavery
"because the South started the war." Therefore they must have done it for some other reason.
You forget that Sherman was speaking of the past. In 1864 the Emancipation Proclamation had been issued so he was right, all the powers on Earth couldn't restore their slaves.
But the Emancipation was *NOT* issued on April 12, 1861. It was issued January 1, 1863. See the problem? "Cause" must precede "effect." No time travel allowed. Conflicts cannot have retroactive causes.
In order for a war to be *about* something, the thing that it is about must exist at the time. It didn't exist until 18 months later, so obviously the war could not have been about Emancipation.
So why was the Union fighting those first 18 months?