Lincoln should have sent them home.

How much agricultural experience did the African peoples that had been kept as slaves have by the end of the Civil War?

After being freed by the 13th amendment, what would have happened if instead of going on to adopt the 14th amendment, these people who had been stolen from their native lands were returned home at our expense?

How would the African continent, and the posterity of those who had been stolen from it, have been different if the knowledge and experiences they had were brought back to Africa instead of only being spread there through imperial colonialism?

Contrast this with the Hebrews that spent hundreds of years in slavery to other nations at different points in their history, and yet that was part of God's plan for that nation.

Jesus' death on the cross, while a terrible sin on the part of those who executed him, was still used by God as part of a plan to bring about an infinitely greater good.

Imagine if the United States had acted less like an empire, bringing more and more nations under its influence, by design or by happenstance, instead focusing on trying to encourage independent strength and national identity in each culturally and demographically distinct people group it made contact with?

We can't change history, but if we can understand the options that were available when past choices were being considered, and seek to understand why one path was chosen over another, and even further to understand why one path should or shouldn't have been chosen over another, then we will be better prepared when faced with similar decisions of our own.

It's also worthwhile to note that God used the evil actions of humans to bring about good for those who remained faithful and obedient to God, while not excusing the evil that was done at the same time.

The Great Commission was to "make disciples of all nations", not to "make the nations disciples" or "unite the nations in Jesus' name."