Several reasons, but the two most important are improved birth care and control of disease. Death at birth was common before the advent of widespread health care, both for the infant and mother. In the past it was common for births to take place at home, with the attendance of a midwife.
Those involved in the birthing would rarely have the expertise to deal with trauma like hemorrhaging or other complications - if anything went wrong the patient would probably die. Now a large percentage of births take place in a sanitary environment, such as a hospital, with the attendance of experts and the ready availability of life support systems for infant and mother. The other big reason for this revolves around the prevention and treatment of disease.
Sanitation, or the management of waste water, was often not handled well in the past, with sewage and drinking water inevitably contacting each other from time to time. This would cause epidemics of such deadly diseases as cholera, diptheria, and many more. Better knowledge about the transmission of disease has led to better control in the form of public education as well.
Something as simple as washing hands regularly, which was unheard of in the past, has helped to control disease transmission. Even identifying that something is wrong and seeking care was not practiced frequently in the past. Such common maladies as appendicitis would likely lead to death before a diagnosis was reached and action taken.
Even if it was, there were no imaging devices that could identify such problems, and the only way to find out for sure would be to perform surgery, which had its own host of problems (see below). Some of the more deadly and common diseases of the past, such as tuberculosis and smallpox, have been largely isolated and eliminated from many parts of the world. Vaccinations undoubtedly have helped to curb the spread of disease.
Disease treatment is much improved today over times past as well, and antibiotic treatment is widespread. Trauma care is a smaller, but also important consideration here. Trauma to extremities of any kind would often lead to amputation, which in turn would often lead to gangrene or other serious infection.
Surgery was not often conducted in a sanitary environment, nor even by trained or qualified individuals. Surgeons would frequently work on numerous patients without even washing their hands in between. If the patient survived the operation, they were likely to die from infection.
Population growth is exponential. There more people there are, the more people there can be. That's reason one.
Then there's medicine/science to prolong life, and food technologies to feed everyone. The latter is v. Important.
Without modern scientific food tech, our population is not sustainable, billions of people would be starving to death as we speak.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.