During the last hundred years the population of the Arab world was doubled more than ten times. This was mainly due to the improvement of health care, education, employment and immigration to the big cities, and sometimes other countries. This change in the population caused a lot of as the number of people is much more than the resources available for them. In the past, there was poor medical care, which led to the death of many people, especially children. The family was used to getting the kids 3 or 4 survive.
This was a major problem till the second half of the 1900's, when the medical care was improved. The improvement of medical care had a positive and negative effect on the Arab world. The positive effect was that the kids of early ages increased which led to the increase of the working labor. This was useful to increase the income of the family, in addition to better output in a lot of jobs. Convincing the families that most of their kids will live - unlike the past was difficult, which led to a rapid growth in population that was out of control.
That was the main negative effect that resulted due to improving the medical care. Another factor that controlled the population growth was education. Men and women became more and more educated and started to realize that it wasn't by the quantity, but the quality. They realized that they would rather get less children in order to be able to give them more care. Unfortunately, this exists only in urban society, where both men and women are more likely to be educated. As for the country side, the tradition of getting larger number of kids is still the case.
Another major factor that affected the population is women's work. Nowadays, women are starting to have their own career and they are less likely to have as many kids as they used to in the past. in many cases, the don't even get any children because they have no time. Also, working women spend less time with their husbands and they are both tired after work so population was controlled through this. However this factor started to exist recently. Finally, immigration to bigger cities seeking better economic and social standard made large cities full of people and the population increased rapidly. This is called urban immigration.
In the other hand people left the countryside and its population decreased. Also immigration abroad seeking better career decreased the number of people in the Arab world. The major problem of immigration is that the people who immigrate are the ones with the working age which leaves the cities with only the old people who can't work and they became a problem to the society.