Answer:
This growth was fueled by the addition of lands throughout the 18th and 19th centuries, through the increasing immigration from European countries, and through the westward spread of American explorers and farmers.
Immigration, birth rates, new territory and the demand for slaves helped the American population to increase by a third every decade
Explanation:
Look into Manifest Destiny, Declaration of Independence, Lousiana Purchase, and the war between Mexico and the US.
