I think it's too easy for the US to build up troops prior to the Civil War. For example, by 1858, I had a stack under Winfield Scott (who keeps getting elected President, by the way, and he cuts tariffs to 10% maximum, which couples with the fact that the AI doesn't shut down technically profitable facilities even though it can't sell them to produce a glut of minerals, iron, and nitrates) that contained 3 infantry corps, a cavalry division, and a Marine division. The stack had power 2000. I built it up just to burn resources because the US had so much money from the gold mines and so many conscript companies. Now this mega-stack can grab Richmond even before the Northeastern Virginia Army activates (not there yet: this is jingoistic bluster). Perhaps a more stringent force limit, including no corps, for the US should be in place before the Civil War. This way, the regular army would remain historically small with the option to expand it somewhat, but not ridiculously so.
I will admit; in hindsight, I should have built up the navy instead, thus burning resources and avoiding this mess. But players may seek to exploit this for gamey purposes.