One reason for this growth was the spread of New World crops like peanuts, sweet potatoes, and potatoes, which helped to sustain the people during shortages of harvest for crops such as rice or wheat.  These crops could be grown under harsher conditions, and thus were cheaper as well, which led to them becoming staples for poorer farmers, decreasing the number of deaths from malnutrition. Diseases such as smallpox, widespread in the seventeenth century, were brought under control by an increase in inoculations. In addition, infant deaths were also greatly decreased due to improvements in birthing techniques and childcare performed by doctors and midwives and through an increase in medical books available to the public. Government campaigns decreased the incidence of infanticide. Unlike Europe, where population growth in this period was greatest in the cities, in China the growth in cities and the lower Yangzi was low. The greatest growth was in the borderlands and the highlands, where farmers could clear large tracts of marshlands and forests.