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The Tarascan State was also a powerful, centralized empire, occupying about 100,000 km2 northwest of the Aztec Empire. They were enemies of the Aztecs, who could never conquer them. They were subdued by /allied to the Spaniards peacefully around 1520 and were more violently subjugated in 1530.
I don't think I remember that since 1500 onwards there were more native political entities in the American continent that were sufficiently centralized so that they could be called "empires".