How were the Mississippian Indians easily defeated by DeSoto?

The Mississipi Indians were easily defeated by DeSoto because they were infected with diseases that had no biological defenses.

Explanation:

When Hernando deSoto and his groups arrived in Mississippi, they began to get involved with local cultures and infect them with diseases (such as smallpox and measles) that the Indians had no biological defense against. This caused a large number of deaths within the native tribes of Mississippi causing a severe collapse in the social structures of the tribes and allowing them to be extremely weakened and easily fought.

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explanation:

fertile good for trade etc