IIUC, The Clone Wars and Rebels animated series are supposed to be Disney-era canon and in continuity with The Mandalorian. However, the portrayal of Mandalorians in each of the three series is wildly inconsistent with the others.
Here’s my headcanon/fanwank attempt at reconciling them:
Centuries (millennia?) ago, the Mandalorians were a warrior culture known and feared throughout the Galaxy. They frequently came into conflict with the Old Republic and the Jedi Order. However, over time, they were defeated, not necessarily so much militarily as culturally. During the long peace of the Old Republic, a culture built entirely on war just wasn’t viable.
The Mandalorians settled down on the planet Mandalore and gradually became a primarily agricultural society. By the time of the Clone Wars, the clan structure, while it still existed, had been weakened, and Mandalore was ruled by a Duchess.
In response, militant Traditionalists formed a terrorist organization, the Death Watch, to undermine the new sociopolitical order and to try to re-establish the old ways. However, like many “traditionalist” terrorists, members of the Death Watch often didn’t actually know all that much about the “old ways” they were trying to bring back, and picked and chose the cool parts (jet packs!) while ignoring the more difficult and problematic aspects (you can’t ever remove your helmet in the presence of another living creature, Mandalorians reproduce primarily if not exclusively by adopting “foundlings” aka war orphans).
Meanwhile, a splinter faction of ultra-traditionalist Radicals didn’t just include those difficult and problematic elements of “the Way”, they emphasized them. They didn’t get much immediate traction, and were a fringe of a fringe, but the successive traumas of the Clone Wars, the fall of the Old Republic, and the rise of the Empire changed that.
A decade after the Clone Wars, the Death Watch essentially won. The Modernist political structure disintegrated along with the Old Republic, and the clan leaders reclaimed power. Most of them followed some form of the Death Watch’s ideology, adopting the cool bits of the Way (rule by clan elders, a warrior ethos, jet packs!) and ignoring the inconvenient bits. Some clans, though, adopted the Radical approach to the Way.
The Imperial Security Bureau interfered in Mandalorian clan politics, in part to divide and conquer, and in part to gather intelligence on the Mandalorian political and cultural leadership. ISB Agent Gideon oversaw these operations, which culminated in the “Night of 1000 Tears”, when the ISB and Imperial Stormtroopers purged Mandalore of clan leaders, Beskarsteelsmiths, other social/political/cultural leaders, and basically anyone who was wearing Mandalorian battle armor. ISB Agent Gideon captured a Mandalorian cultural artifact, the Dark Saber, during the Purge, and for his efforts was promoted to Moff.
Most “Mandalorians” were just farmers trying to get by, and most of them just kept their heads down during the Purge, got on with farming, and tried to survive. Some Traditionalists fled to the Fringe and the Outer Rim, and made their way as bounty hunters and mercenaries. Some Radicals also managed to flee, establishing “Coverts” on planets in the Fringe and Outer Rim, and tried to maintain “the Way” while surviving as bounty hunters and mercenaries.
The Empire mostly ignored the surviving Mandalorians as long as they just worked as individual free-lancers; it was only when they discovered a functional Mandalorian “covert”/colony that could serve as a point of organized resistance that the Empire would act against them. To survive, the Coverts adopted a policy of only allowing their people to go out and act as individuals, and to conceal the existence of their Coverts, which they continued even after the fall of the Empire and the establishment of the New Republic, since Imperial Remnants continued to persecute them and the Republic were traditional enemies.