The Galran Black Army were the main troops of the Galra empire. They were under the commander of Sadak until his death upon which Daibazaal took over the duties as leader.
Comparisons to Voltron
In Voltron, the Black Army soldiers were called Ultra Droids, and said to be robots. This was no doubt helped by the Black Army's shining metallic skintone.
Due to this change, scenes of the Black army being violently killed were taken out in Voltron. The sadism of the Black troops was also toned somewhat, and while they still used whips to threaten slaves, they're more extreme inhumane acts of cruelty were cut.