I would add: they wanted to keep European powers like Britain and France out. With both having already abolished slavery it would be politically very difficult for either to intervene on behalf of a country, the CSA, which still had slavery.
Also, Lincoln and his corporate fatcat supporters started this war over money. Even a cursory reading of the major Northern Newspapers as well as Lincoln's insistence on collecting duties in Southern ports in his inaugural address makes that quite clear. They thought it would be easy....a mere matter of marching. Remember that they only called for 75,000 volunteers and only for a period of 3 months. Then their little war over money turned extremely expensive and turned into a bloodbath.
Now there are a lot of parents of Northern sons grieving for the loss of their son and even more who came back mangled and crippled for life. What do you tell those people? They are voters! Do you tell them that their loved one was killed or had his arm blown off over......money? Sure its true but those voters are going to be absolutely furious when they hear that. So now Lincoln and indeed the whole Republican Party establishment now need to wrap this bloodbath in the cloak of some noble cause to make it more palatable. They know the voters back home won't look too closely. They desperately want to believe the frightful price they paid was for some noble cause. "dying to make men free" fits the bill nicely. Who cares if anybody who bothers to look at what they were saying in 1860 and 61 can immediately see that its pure BS?
Unquestionably they misjudge Southern discontent and willingness to fight for Independence. And yes, once Lincoln's ill conceived war turned into a horrible disaster, they had to go searching for some better justification than "preserving the Union" that didn't want to be preserved.
Now there are a lot of parents of Northern sons grieving for the loss of their son and even more who came back mangled and crippled for life. What do you tell those people? They are voters! Do you tell them that their loved one was killed or had his arm blown off over......money?
They didn't breath a whisper of that. They always presented it as "Preserve the Union" being a somehow requirement. As I have pointed out many times, the US allowed the Philippines to leave, they allowed Cuba to leave, and there is still an open invitation for Puerto Rico to leave. These places didn't have any money, and so there was no great financial loss to the Northern power structure if they left. The South was different. If it were allowed to leave, it would directly challenge the Northern economic power structure economically.
This Northern economic power structure, (robber barons as they were later known) would not have it!
They know the voters back home won't look too closely. They desperately want to believe the frightful price they paid was for some noble cause. "dying to make men free" fits the bill nicely. Who cares if anybody who bothers to look at what they were saying in 1860 and 61 can immediately see that its pure BS?
And the strategy is still working today. Most people bought the sales pitch, and never bother to look under the hood. Part of this is because "group think" makes challenging the official dogma a reason for shunning in polite circles. Group think is self reinforcing because of social peer pressure, and so few people have the temerity to challenge the official account of what happened and why.