Ok, they held unwilling captives on their ships in chains until they could get them to market to sell them for money. Let me think on this. Kidnapping and selling a human beings into bondage vs. buying and caring for a human being while they are in bondage. Neither is humane. Neither is acceptable but in the time it was happening, it was legal. This is still going on in other parts of the world but the only place that gets a finger pointed at it and is constantly cursed because of it is the Southern part of the United States. How much more inhumane is slavery than say, working a child of 6 years old for 12 hours a day in nasty conditions? Is is any worse than allowing women to sit at sewing machines for 10 to 12 hours a day with very little heat in the winter and no cooling in the summer? Oh please tell me it's more humane than soldiers coming into a camp of families and killing all of them just because they can and oh, the government wants the land they own. Can't be more humane than using laborers from the Far East to build railroads under a broiling sun and paying them less than scale. Oops, forgot, there wasn't a 'scale' wage at that time. Could that have been any more humane than taking women who were noncombantants working in a mill weaving fabric to a town square close by to be kept in a pen before they were put on trains to go north with no real destination and many were never heard from again? Yes, I agree, it's really less humane than rounding up all American citizens of Japanese origin just because America goes to war with Japan. After all, Japan started it.
Can you honestly say you think the United States Government has ever really cared about humanity? Nope, it cares about the almighty dollar. That's it's bottom line.
The United States Government did NOT want to lose one dime of revenue it took in so it decided that leaving the Union by a dues paying member was not acceptable. That's the bottom line.