On the planet Dathomir, women were revered as leaders and rulers, while males were treated as slaves and mates. Hardly any of the population still living, less than a hundred actually, and most of these had been imprisoned or executed by the evil Nightsister Gethzerion.
The Nightsisters were a sect of Force users, but had to chant and perform rituals to channel their powers into something tangible. Although it was Gethzerion who came to realise that the rituals and chanting did not aid them. They could use their powers without them, and did so. They used the Dark Side to attack other sister clans, while Gethzerion worked solo, bending others to her will.
When Palpatine was alive, he knew about Gethzerion and her sect. He allowed her to live, knowing that she was powerful, but only as long as she stayed on Dathomir. On the planet was an Imperial penal colony for political prisoners, but to keep the Nightsister on Dathomir, Palpatine had the orbiting airfield destroyed. This kept the Nightsisters from going into the galaxy, but it also trapped many Imperials on the planet. These were later killed or imprisoned by Gethzerion.
For many years no one came to Dathomir, afraid of the Dark Siders that resided on the planet. While travelling through the Quelii Sector in the Star Destroyer Iron Fist, Commander Zsinj was ordered to watch over the planet. This was not the most glorious of missions, but when Palpatine was destroyed, Imperial leaders fought for power, and Zsinj became a warlord. He landed on Dathomir, and made a pact with the Nightsisters.
Gethzerion desperately wanted to leave the planet, and saw her chance when Han crash-landed the Millennium Falcon on Dathomir. At the time, Solo had a Hapan bounty on his head, and Zsinj was eager to claim it. He contacted Gethzerion, who offered the help of her Nightsisters in exchange for a ship. Zsinj agreed, but Gethzerion found capturing Han and Leia more difficult than she had first thought. For one thing, Teneniel Djo of the Singing Mountain Clan was against her, and then Luke was trying to protect his sister and friend. Gethzerion called Force storms and other Dark Side powers against Luke and the Nightsisters of the Light Side, but they all failed.
Seeing that there was no way she could win, Gethzerion fled. A space carrier was taking off for Zsinj's ship, and Gethzerion managed to scramble aboard. Han followed the ship in the Falcon, and when the carrier's missiles proved ineffective, Han armed his own and destroyed the carrier, rather than allow Gethzerion to spread her powers throughout the galaxy.
With the Gethzerion gone, the Nightsisters came out of the shadows and practised their Light Side powers instead. This was how it should always have been, and with the source of evil gone from their lives, it is how it will always be.