I’m not a fan of Lincoln, I was simply pointing out that as far as he was concerned he was waging war against fellow Americans. He never regarded the CSA as a separate nation, they were just Americans who deserved to be killed if they believed that they could secede.
You know perfectly well Lincoln believed the Confederate army had to be defeated and destroyed, but only after Confederates first provoked, started, formally declared and began to wage war against the United States.
Late in the war, at Hampton Roads, Lincoln conferred with Confederate representatives, offering them peace and compensation for freed slaves.
They refused immediately, preferring to fight on until unconditional, uncompensated surrender barely two months later.
It was their choice.