Why did many American Indian chiefdoms came to an end within a few years of Hernando de Soto's arrival in Georgia

Hernando de Soto's was a Spanish conquistador, a conqueror, he was a very ambitious and powerful man. In 1538 he left Spain with more then 700 hundred man and later on, after passing thru Cuba, landed in North America. De Soto's ambition led him to search for more gold in North America, and as he crossed the lands he encountered many Native Americans, which were made prisioners along the way. As time went by they suffered other sort of attacks by the Native Indians, which led to a bloody battle where many Indians were killed.