Why US has increasing population?

Today in Human Geo, we went over three key terms. Migration, pull/push force, and total fertility rate. In migration, there is immigration and emigration. Immigration is when someone enters a country and pretty much lives there. Emigration is when someone leaves a country to move to another country. The difference between the two for a country is the net migration rate. Next, a push force are reasons why people emigrate to another country. For example, religious persecution, lack of job opportunity and bad living environment. A pull force are reasons why people want to immigrate to a certain country. For example, religious freedom, job opportunity, better living conditions. Finally, total fertility rate is the amount of babies a woman has. This means if a woman gives birth to a child who lives for at least an hour, add one to the total fertility rate. The amount total fertility rate to have a population stay the same is 2.1. The reason its not two is because children die as children so obviously that decreases the population. For the United States, why does the population increase especially since the total fertility rate is below 2.1. This is where all 4 terms comes together. Many people migrate to the Unites States because it is a free country with many job opportunities and the total fertility rate is only .04 lower than the average.