First again!

...Or, maybe not. :p

Here's a quandary that's been bugging me for a little while. I fear I may have committed some badhistory (or bad geopolitics, but I'll get to that later) myself, but I'm not sure. This didn't happen on Reddit, though, and I thought it would be in bad taste to make a whole thread dedicated to the matter. Thus, I thought our latest 'Mindless Monday' would be appropriate, at least looking at the lax rules for these threads, though of course, mods, please feel free to delete this if it’s troublesome. I was having a conversation with an acquaintance over the subject of the American Civil War, and he brought up an argument I had honestly never heard before. To summarize (hopefully without doing injustice to what he said), it went something like this:

“Slavery wasn’t worth fighting for at all, but here’s something Northerners don’t think of very much: If the Civil War was justified to “end slavery,” why isn’t any American intervention justified if the reason is “good enough?” Should we invade Nigeria to stop Boko Haram (our girls haven’t been brought back yet!) You’d probably say no. But when it comes to Southerners, who you Northerners keep saying are worthless embarrassments the US would be better off without, you still can’t let them leave. So how can you justify intervention to stop slavery but not to stop terrorism or misogyny or whatever? It seems like you just have it out for Southerners specifically.”

Like I said, I hadn’t heard this argument before, and I had to admit he had a point. It’s easy to get on board with a war against slavery, but it’s also easy to get on board with wars against terrorism or maltreatment of women or a lot of other ills, and it’s something to be careful of. Still, upon considering it, I ended up thinking that the North would still have been particularly justified in attempting to subdue the South. Here’s what I replied:

“True, but think of what would have happened if we’d just let the South secede. Pretty much all the seeds of conflict would still be there. Slaves would still try to flee from the South, leading to a lot of acrimony between the old nation and the new one. The South was also pretty aggressive and expansionist; look at the Mexican-American war. It’s likely a separate Confederacy and Union would have come to blows later on even with a peaceful secession. Southerners might be annoy us Northerners inside our Union, but they’d be outright dangerous outside of it. That's why you couldn't justify other forms of intervention through this reasoning, by the way--as bad as organizations like Boko Haram may be, they're far away across the ocean instead of right next to us like an independent Confederacy would have been.”

I don’t want a brigade or a personal army or anything like that (that’s why I’m being vague about who I was talking with and where), but I would be interested in hearing from folks who know more about the geopolitical/strategic setting of mid 19th century America than I do. This was just an off the cuff conversation, so I probably didn’t hew to Rule 5 as much as I could have or should have, but I’m wondering, was my reasoning completely off? If Lincoln had just let the South peacefully secede (I know, he wouldn’t have), would a large conflict (or series of conflicts) between the US and the Confederacy be likely in the future, or was my assessment too pessimistic? (This is a ‘what if’ question too, which is another reason I took it to a Mindless Monday thread rather than, say, an askhistorians thread. :p )