why do people migrate

There is two causes that push people to migrate they own country.
1. Push forces. example:
 - civil war
 - environmental degradation
 - unemployment or underemployment
 - religious or ethnic persecution

  2. Pull forces
 - better economic opportunity
 - better heath services
 - religious freedom
 - political freedom.
 
 The total fertility rate is the average number of children born per women.
For a population to remain the same, the TFR must be 2.1.
If it is higher than 2.1 the population rises
If it is lower than 2.1 the population falls
World TFR is 2.42