Re: Black Magic.
Well, Islam has taught us that our souls are all portions of God’s soul, correct? Now there are certain practices, or rituals, you perform (involving sexual acts and/or blood usually) to establish communication with jinn. I am not sure if the ritual itself allows them to make the interdimensional “warp” to our dimension/universe or if it’s the actual pact you create. But once you have communicated with a jinn, you’re selling your soul to the jinn in return for their services. In doing so, you are also selling a part of God’s soul and therefore permanently barring you from ever entering Jannah.
Jinn, like Shaitan (keeping in mind that Shaitan himself is a jinn), have the ability to get into people’s minds and influence our thoughts at their will. Once you understand that concept, I’m sure you can imagine how they can create tensions between husband and wife, family, friends, siblings, or anyone.
*Edit - I hope Allah (swt) forgives me if I have made any errors in what I posted.