Massallah pertaining to making Nikaah with slave girls

Slmz, i have a question thats been troubling me and maybe you can shed some light.
The following verse : “And those who guard their chastity (i.e. private parts, from illegal sexual acts). Except from their wives or (the captives and slaves) that their right hands possess[…]”
Why is relations with slave girls allowed?

I thought nikah was the only halaal way to have intimate relations.
Does islam or did islam not see slavery or these relations as bad?
Please explain this verse as i do not understand it.
thanks