It was interesting seeing you mention a Union Army ancestor.
The book/movie Gangs of New York shows how the Union Army enrolled Irish immigrants right off the boat in order to fill their ranks with imports who would be willing to kill Americans.
The Union Army had a hard time getting actual old line Yankees to do the invading and killing as the war wore on, witness the July 1863 draft riots of NYC. Lincoln had to make do with recent arrivals as well as the communist ‘48ers who had been enthusiastic revolutionaries all along.
First of all, there were plenty of volunteers in the early days of the war, and very many of them were "actual old line Yankees." But it was a long war and a lot of troops were needed to win it, so the US resorted a draft, as did the Confederacy.
There were stories of rich men or ambitious men on the way up in business, who hired subsitutes or got out of the draft in other ways, but they were the exceptions, rather than the rule. Those draft riots mostly involved Irish-Americans who weren't keen on the draft, not "actual old line Yankees".
Mine didn’t murder or kill. He served his country and was a literate man. Very much so.