actually, even in the 1st world, we are much better off going for as long as possible, up to 2 years. 
When a baby is born, its immune system is really undeveloped. As such, IgE that is passed in the mother's milk protects the baby. 

20 years ago, this was not a big deal because we had decent antibiotics. Right now, we are in DEEP trouble because we are at our last line of defense WRT antibiotics. A number of bugs are becoming resistant to EVERYTHING that we have. 
So, the longer that you can go, the better for the baby, as well as society.