Final answer:
The factor likely to cause virtually all population growth in the United States in the next few decades is net in-migration.
Step-by-step explanation:
The factor likely to cause virtually all population growth in the United States in the next few decades is net in-migration. Net in-migration refers to the number of people moving into a country minus the number of people leaving the country. In the United States, net in-migration has been a significant contributor to population growth, particularly in recent years.
For example, in 2019, the United States saw a net in-migration of approximately 595,000 people. This means that more people moved to the United States than left during that year, contributing to population growth.
Net in-migration is influenced by various factors such as economic opportunities, political stability, and family reunification. It plays a crucial role in shaping the demographic trends and population growth of a country.