The world we live in is a dark place as it is full of unbelief. In this world of darkness, Satan has greater access into the hearts and minds of people.
What are principalities and powers? It speaks of angelic powers of which there are bad, Satan is their head. These demonic hosts wage war against the saints and the church.
Eph.6.12For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.