I do not believe famines are caused by anything other than abnormal conditions. They were hardly deliberate,although unintended consequences might have played a role. I think you underestimate the role of climate in famine and also up until probably the mid 18th century there was a lack of a marketing structure to mitigate famine. There are many studies suggesting volcanic activity, severe el nino events, and climate changes all contributed to famines.

As an example a paper on the impact of volcanic activity from ice core analysis and correlation with medieval documents.

http://web-static-aws.seas.harvard.edu/climate/seminars/pdfs/mccormick_07.pdf
and

Famine during the little ice age