The crisis of 3189 and 3190 caused by the Dark Matter Anomaly, a moving gravitational force that destroyed Kwejian and threatened Earth and Ni'Var.
The Dark Matter Anomaly was a huge, moving gravitational disturbance that appeared in 3189, destroyed the planet Kwejian and threatened many more worlds. Starfleet found that it was not natural. It had been built by an unknown species from beyond the galactic barrier, later called Species 10-C, as a tool to harvest a rare material.
The scientist Ruon Tarka wanted the anomaly's power source for his own ends. He joined forces with Cleveland Booker to destroy it with an experimental weapon, against the Federation's wishes. Their attack only led Species 10-C to create a new anomaly, and it set course for Earth and Ni'Var.
The USS Discovery crossed the galactic barrier to make contact. Tarka tried to seize the power source and was killed. Discovery's crew then explained that the Federation meant no harm, and in 3190 Species 10-C shut the anomaly down and agreed to stop using such tools.