Sauron forged the 1 ring to control the other 19 ones. He put a lot of his own power into it, which made him very vulnerable.
- The Dwarf rings failed and he had to recall them
- The Elf rings were not under his influence, but did get to use his power anyways to establish Rivendell & Lothlorien
- The Human rings got him the Nazgul, terrifying creatures that did nothing to help him in LotR
- Creating the One Ring led to his destruction