From Destinypedia, the Destiny wiki
The Plaguelands is an area near the Cosmodrome that has been quarantined for centuries. After the Devil Splicers had broken through the walls and found SIVA, they began using the forbidden technology to transform this region of Old Russia to fit their twisted desires.
The Plaguelands also connects to remodeled versions of locations from the original Cosmodrome Patrol area:
List of appearances