The Mandalorian is finally introducing more Mandalorian characters, which also means covering their planet's greatest tragedy: the Great Purge. First referred in season one, the Great Purge is a huge part of Star Wars history, tied not just to Din Djarin's backstory, but to the whole era of the Empire.
It's been hinted on and off throughout The Mandalorian that something truly terrible happened to the people of Mandalore under Imperial rule, and it's even been referred to as "the Purge" or "the Great Purge." Although the live-action Star Wars movies have never addressed this plot point, the animated shows — particularly The Clone Wars — detail the politics and fall of Mandalore with plenty of specifics.
In The Clone Wars, the complicated politics of pre-Imperial Mandalore are on full display. While the pacifist Satine Kryze rules the planet in the years before the Empire's takeover, a militant sect called the Night Watch — which includes her own sister, Bo-Katan, who has begun appearing on The Mandalorian — wants to restore the planet's ancient military culture. The result, unfortunately, is the splinter group getting betrayed by the Sith lords they allied with and a long power struggle on the planet. When the Jedi Purge happens, as seen in Revenge of the Sith, the Empire occupies Mandalore, and despite some resistance, enough clans betray Mandalore to allow the Empire to take control.
Despite being ruled by the Empire, the Mandalorians never stop resisting, and at some point, the Empire decides it's not worth the struggle anymore and that they're unlikely to ever fully control the planet. Instead, they initiate the Great Purge. The exact specifics of how or when this happens aren't clear, but the results are: nearly the entire Mandalorian population is wiped out by the Empire's genocide, and the handful of survivors that do make it out go into exile underground (literally).
Not only did the Great Purge essentially destroy the Mandalorian people and its planet, but it also meant that the Empire took control of some of the planet's greatest treasures. In the first season of The Mandalorian, Din Djarin learns that a large quantity of beskar, the metal that makes up Mandalorian armor, had been seized by Imperials and taken to forge their weapons. Even more significantly, the most iconic weapon of Mandalore, the black-bladed lightsaber called the Darksaber, was somehow lost too. It was previously held by Bo-Katan, but disappeared under unexplained circumstances during the Purge and has since reappeared in the possession of Moff Gideon. One thing seems for sure: Mandalore's history is playing a key part in the main drama this season!