Some Civil War historian claimed the Union was fighting with one hand behind its back. The South was at maximum effort while the North had plenty of capacity, men and material it could use if needed.
Shelby Foote said that in Ken Burns’s documentary.
I think that is correct in terms of men, material, and logistics. The south and Lee never had a realistic chance of a conclusive military victory to back up the right of succession. It still would have been interesting to see what may have happened in terms of a settlement if Lee had prevailed at Gettysburg and had been able to flank Philly, Baltimore and/or Washington D.C. .
Yet they had to draft immigrants as soon as they came off the boat. Somehow, that doesn’t suggest they weren’t starving for manpower.