At first the Portuguese had good relationships with the Kingdom of Kongo. It was the Civil War within Congo that would make many to be eventually enslaved and sold to the Portuguese and, later on, to other Europeans.
On the other hand, mass slavery was never really a practice of the Persians. Slaves existed, but mostly, they had prisoners of war in a semi-slavery situation and and in many cases, their lives were still better than those of the commoner.
At the beginning of the 19th century, Iran imported some white people as slaves from Russia and sold them at the bay. They also sold black slaves from East Africa.