what is the reason of increasing population of developing nations???

I am not sure if I understand your question... But developing nations are the same than non developing nations. They have not yet learn the benefits of curbing their population. It is capitalism which stops people having children. Once you start earning some real money... and you see the possibility of buying a house... you have to make a choice... 8 children... or 2 children and a house. People in the West choose to have a house rather than a lot of children. They prefer to be rich with two children rather than poor with eight children. It makes perfect sense to me. As for the population being stable in developed countries... It should be... but is not really. Thanks to immigration... we have 1000 people arriving in Australia every week. And it has been like that for over 20 years. Australia's population has doubled in the last 30 years... mostly because of immigration.