(Most bread was rye, "Let them eat cake", which was made with wheat flour, was not so callous as often presented).
A probably significan factor in the French Revolution was the major eruption in Iceland of the Laki Fissure in 1783, it caused serious climatic disturbance in all of Europe, and our very own Ambassador Benjamin Franklin attributed this strange weather to an eruption in Iceland.
This weather caused serious crop failures and famine for several years. It may have contributed to Ergot fungus as well.
Many people think that ergotism was a big factor in the Salem witch hunt.