Lekor

Pre-First Order
Lekor used to be a peaceful planet after the Empire was vanquished, but the First Order took hold of its excessive amount of Kyber Crystals and turned it into a mine / base. It has been such ever since.

Star Wars: The Fall of Lekor
The Knights of Ren and Jedi fought on Lekor's moon, Urygen, then moved to Lekor where they fought in the First Order base. The battle destroyed the base on Lekor.