It is ironic that the 20 rings in The Lord of the Rings are a complete mystery to most fans, who tend to limit their experience to the movies. It wasn’t until Amazon’s The Rings of Power series that some began to understand that they played a much more important role than they imagined. They provided preservation, increased natural power, and a special connection to the One Ring, but that’s just the tip of the iceberg.
“Three Rings for the Elven-kings under the sky. Seven for the Dwarf-lords in their halls of stone. Nine for Mortal Men doomed to die. One for the Dark Lord on his dark throne in the Land of Mordor where the Shadows lie. One Ring to rule them all. One Ring to find them, One Ring to bring them all and in the darkness of the Land of Mordor where the Shadows lie.”
We know that the 9 Rings of Men worked perfectly because the Nazgûl exist and because the Elves guessed Sauron’s plan when it was set in motion and found a way to benefit from its powers. Furthermore, these three were created by Celebrimbor without Sauron’s direct intervention. And what about the dwarves? Why did they not fall under the control of the Dark Lord? Why are there no Ringwraiths of this race? Well, there is an answer.
The Seven Rings given to the dwarves did not fulfill their purpose of control, but they did affect them to the point of ruin. Sauron overlooked or forgot that the dwarves were created by Aulë, the Vala blacksmith and craftsman, with exceptional physical and mental endurance and a particularly strong will against the forces of darkness. They were neither subjugated by the control of the One Ring nor did they benefit from unnatural longevity, but it did affect them psychologically and turned them into insatiable beings.
They are a race of stone, persistent, quick to friendship and enmity, and they endure fatigue, hunger, and bodily wounds with greater strength than all other speaking peoples; and they live long, much longer than Men, and yet not forever. – The Silmarillion
The Dwarves were not easily subjugated to any foreign will… They did not become invisible, nor was their life prolonged. Only an unbridled greed for gold and precious things was awakened in their hearts. – Appendices to The Lord of the Rings
The power of the rings made them a race prone to finding riches, which gradually led to excessive greed and isolationism, which is even mentioned in the movies. If you’ve seen The Hobbit trilogy, you’ll remember that Balin and Bilbo describe the greed of Thorin’s family as a “disease of the mind” or “curse.” This does not mean that the dwarves were bad or evil, far from it, as they became legendary craftsmen and architects, and many saw that something was not right with their people.
There was a gleam in their eyes that one often sees in men who have lost their reason; as if some strange sickness had clouded their judgment because of the gold accumulated by their ancestors. – The Hobbit
In the end, the blow suffered by the dwarves was twofold: Sauron struck the dwarves with particular viciousness and force because of their resistance to control—think of the battles of Moria and The Lonely Mountain, among others—and greed finished them off by attracting dragons to their doorsteps. Not to mention the Balrog they awakened in the depths. So much so that four of the seven rings were consumed by dragons and the remaining three returned to Sauron’s hands.
