Answer: African Americans
Explanation: African Americans are the among large groups in the United States that are present. African Americans are mostly ancestor of Africa and also many had ancestors that were in non black community. The ethnic group of African-American had a low rate of fertility while the times of eighteenth century because in that time they were already facing some severe conditions and had to go through variation in fertility condition.
These condition started to reduce when there was declination towards the mortality rate.