As I was listening to 1A talking about the 1619 project this morning I remembered this question (and the list of questions it creates) I have long had.
What led to the abolition of slavery in other countries?
Where wars/battles fought to end slavery?
How did the general population take this change, and how did it affect the country as a whole?
Where there countries that allowed slavery in their colonies but not in the motherland?
These are huge, sprawling questions that are beyond the scope of a single r/AskHistorians post. While you are presumably referring to New World enslavement of people of African descent for (primarily agricultural) labor purposes, keep in mind that "slavery" as a general concept has existed in various forms throughout time and place, with Mauritania becoming the last country to ban slavery in 1981. Even after European countries banned slavery, forced labor in colonial empires existed throughout the 1800s and 1900s.
To get answers to your questions, think about what areas or time periods you most want to know about to construct a more specific inquiry.
You should also check out r/AskHistorians FAQ, as slavery is a well-discussed topic and you may find lots of your questions answered already. https://www.reddit.com/r/AskHistorians/wiki/faq/politicsandphilosophy#wiki_racism_and_slavery