Population including migration

Today in human geography we learned about measuring population. we learned that RNI stands for rate of natural increase and you come up with the RNI by subtracting the death rate from the birth rate. We also learned about the net migration rate which is the difference between the number of persons entering and leaving a country during a year. We followed this up with net immigration, which is the excess of persons entering the country. Then emigration which is the excess of persons leaving the country. So why would people migrate? Well due to the push and pull factors, push factors include civil war, environmental degradation, unemployment or underemployment, and religious freedom. some pull factors are better economic opportunities, better health services, religious freedom, and political freedom. On the other side of all of this there is the TFR or total fertility rate is the average of number of children born per women. For a population to remain the same it must stay 2.1, anything lower population will fall, anything higher population will rise.