Star Trek: Everything We NOW Know About The Burn

Before the events that led to the Burn, the Milky Way Galaxy was facing a shortage of Dilithium, inspiring the Federation to look into other methods of transport. It decreed that all of its member worlds should make an effort to discover a new, safe form of propulsion. Ni'Var, formerly known as Vulcan, came up with SB-19.

This discovery would allow starships to move across vast distances via subspace and proved to be the most promising alternative to Dilithium. However, Ni'Var's scientists determined that the risk of SB-19 was too great to continue the experiments and attempted to shut them down.

Nearing desperation, the Federation refused them permission to do so. The resulting Burn was, for a time, believed to have been caused by SB-19. This led Ni'Var to secede from the Federation, removing the Vulcans, a founding race, from the alliance. The Romulans, who by this time had established their home with their Vulcan cousins, voted against leaving the Federation, but were outnumbered.

For more than one hundred years, Ni'Var remained separate and cordially hostile to the Federation. When investigating the cause of the Burn, and armed with the black boxes from ships destroyed therein, Burnham and the crew of the Discovery were able to determine the point of origin for the event, ruling out SB-19 as a possible cause.

This finally allowed relations between Ni'Var and the Federation to thaw, leading to the former's eventual decision to rejoin the organisation.