The Kingdom of Benin and the Ashanti Empire were the main suppliers of slaves to first themselves, then the Arab and European markets.
Their wealth was originally from gold. This was used to fund large and efficient armies that preyed on the small tribes and kingdoms.
The wealth gained – as with all empires – went into producing luxury and art for the ruling classes.
I know this is an attitude which is unfashionable but we all have to take responsibility for our ancestors’ actions. Things are rarely one sided.