Please bare with me here, but this is man's thinking and not the examples left to us in the Bible.
In Roman's Pauls said that God raises up whom he will for his purposes. That Governments are established for only one purpose and that is to establish peace by which the word of God can be spread. For this purpose God tells us to be content with our station in life and to do his will no matter what the circumstancess are that we find our self in. Whether it is as the master or as the slave. To this end most Black churches in the South trace their start or origin to the plantations life and the Plantation owners.
In Philamon Paul under arrest in his home comes in contact with a runaway slave by the name of Onisimus. Under Roamn law Paul could have done with Onisimus as he pleased. Paul converted the runaway slave and sent him back to his former master Philamon.
In Jeremiah Chapter 37, God said that he would bring judgements down on any nation that opposed King Nebuchadnezzar because he was going to use Babylon to punish the nation of Judah for their unfaithfulness. Does that mean that God was for the wicked King Nebuchadnezzar? No. It means that God uses all things, including Kings and Kingdoms, to achieve his purposes no matter what the earthly outcomes are.
In the Old Testament God used ungodly nations to punish Isreal for their misconduct and lead them back to his purposes. This doesn't meant that God was for ungodly nations. Nor does it meant that the victor of every war were God's chosen people.
Now what does all of this mean?
If there is a spiritual purpose to be gained from the American Civil War, I believe it is this.
That after the Civil War our Government changed to become a strong centralized government. For better or for worst it is that strong centralized Government which put an end to the fractional attitudes of the individual states. The results was that it was the strenght of the United States that won World War II and stopped the Nazi extermination of the Jews. It was the United States and Great Britian that established the new nation of Isreal under a joint Resolution of Parliment and Congress in 1946 regarding the relocation of the displaced Jews of Europe. Isreal became an independant nation in 1948 and the United States has been Israel's friend since that time.
It is that reforming of a nation of Isreal, which was foretold in the Bible, that is the ultimate greater biblical purpose, which I believe the United States came into this world in 1776, to be the world power that it did became, to do in the first place.
Again just my two cents worth.