Sabine is human, like most Mandalorians, and comes from Clan Wren, which is a part of House Vizsla. The head of that House during the Clone Wars was Pre Vizsla, founder of Death Watch. This was in an era when Duchess Satine Kryze, the ruler of Mandalore, instituted reforms that restructured the historically warlike Mandalorian culture into a peaceful one, with nary a T-shaped visor in sight.
Pre Vizsla and his followers vehemently opposed these changes, and attempted to preserve and rebuild the warrior culture of Mandalore. They also used terroristic tactics in an attempt to take over Mandalore by force. As a member of House Vizsla, Sabine’s mother Ursa Wren was a member of Death Watch and believed in their cause. Not all Death Watch members were part of House Vizsla, however. In fact, Duchess Satine’s sister Bo-Katan Kryze was also a prominent member of the faction.
In their efforts to take control of Mandalore, Death Watch allied themselves with the Sith Lord Darth Maul, a compromise that some members, including Bo-Katan, found unacceptable. Ursa Wren helped Bo-Katan and her allies, including Ahsoka Tano, retake control of Mandalore from Maul and the corrupted Death Watch. Before long, however, the Republic became the Empire and Mandalore was under its heel. Gar Saxon, a former ally of Maul, became Imperial Viceroy of the planet, and an Imperial Academy was established there.