An international organization, headquartered in Geneva, Switzerland, created after the First World War to provide a forum for resolving international disputes.
Your answer is that the main reason is that people buy land and they needed to get money which means there really greedy people so the buy slaves and force them to work for little or no money so they can sell crops (they made the slaves become farmers) to make profit then they would buy more land and get more slaves to work as farmers on and on. So it spread because one guy did it and he made a lot money and other people wanted to do the same and that's how slavery spread through North America.
