What is demographic transition? What causes it? Why is the process (of demographic transition) different in contemporary developing countries than it was in currently developed countries? (i prefer...

What is demographic transition? What causes it? Why is the process (of demographic transition) different in contemporary developing countries than it was in currently developed countries? (i prefer the answer base on the book ” Todaro, M. P. and S. C. Smith, Economic Development, 12th Edition” thx