Complex sentence: The tribe increased in number considerably during this time, and was further supplemented from the late 18th century by the Black Seminoles, free blacks and escaped slaves who settled in communities near Seminole towns.
Split into simpler sentences: The tribe increased in number considerably during this time. Beginning in the 18th century, they were supplemented by the Black Seminoles, free blacks and escaped slaves of African descent who settled in communities near Seminole towns.