Answer:
because they appeared to be assimilating to Anglo-American norms.
Step-by-step explanation:
The term "Five Civilized Tribes" came into use during the mid-nineteenth century to refer to the Cherokee, Choctaw, Chickasaw, Creek, and Seminole nations. ... Americans, and sometimes American Indians, called the five Southeastern nations "civilized" because they appeared to be assimilating to Anglo-American norms.