More outside support including money, food, health care and infrastructure. Better education, disease control, no large conflicts going on at the moment-there's plenty of war going around but just in a smaller scale.
See like in INDIA there has been a huge population explosion and the causes are several ILLITERACY well several people are illiterate and so they count each child as two hands for help and not as a stomach to feed . then the society is PATRIARCHAL and many still believe a son to be a boon and due to practises like DOWRY people have several girl childs to have one boy.then one big reason is POVERTY when more than 50% population is below the poverty line so good education is very hard to come by. then there is UNAWARENESS of FAMILY WELFARE PROGRAMS etc I don't want to write an essay so i have mentioned some key points
We have people all the time getting pregnant accidentally and against their own wishes even here in the U.S. where we are well educated about these things and where any number of birth control devices are readily available. Imagine how much more rampant the problem must be in nonindustrialized nations with little or no education, no laws regarding underaged sex, and no birth control.