Between 1950 and 2000, a period of 50 years, the world population more than doubled, from 2.56 billion to 6.09 billion.  Most of that growth was in the less developed countries where the population grew from 1.7 to 4.9 billion.  The population of India increased 3.5 fold, and that of China increased 2.5 fold, which combined added another 1.4 billion people to the world.

The slowest growing countries were in Eastern Europe where growth was either flat or less than 10%.  The population of Russia actually decreased during some of those years.  Even Belgium, Italy, the UK, Portugal, Austria, and Denmark experienced growth rates of less than 20%. The 2.1 fold increase in the US population was quite a bit higher than in Europe, but the total growth in China and India dwarfed our total population by five fold. 

Many of the fastest growing countries during this time were Arab and African countries.   The population of the United Arab Emirates increased 84 fold, of Qatar 29 fold, and of Kuwait 24 fold.  The populations of Namibia, Benin, Niger, Liberia, Sudan, Senegal, Swaziland, Cote d'Ivoire, Togo, and French Guiana increased more than seven fold.

It's ironic that many of the countries with the fastest growing populations are also the ones with the shortest life expectancies, and vice versa.  The life expectancy of men in Rwanda is only 33 years, but their population increased almost five fold, whereas the life expectancy for men in Japan is 80 years, but their population increased only 50%.

Twenty million of the 124 million increase in our population was due to immigration, which means that immigrants accounted for 16% of our total population growth, many of them illegal aliens.  Had it not been for them, our population would have grown only 68%.