The Black Mesa Incident, or referred to once in-game as the Lambda Incident, is a catastrophic event resulting from an experiment carried out at the Black Mesa Research Facility, which results in a Resonance Cascade, and ultimately the invasion of Earth by the Combine. Its aftermath sees the teleportation of multiple races of extraterrestrials into Black Mesa; the resulting battle between the base's personnel, human military forces and Xen creatures conclude in the complete destruction of the facility and the death of almost all of its residents.