I posted this a while back (four years ago! time flies) about the volcanic eruption of Mt. Tambora, noting that the ash it spewed into the atmosphere was responsible for what we call "the year without a summer."
Turns out, according to Slate, Tambora was responsible for more than just a really snowy June. Scientists have linked (indirectly) the worldwide cholera epidemic of the early Victorian era, the Opium trade in the Golden Triangle (and by extension the Opium Wars) and the British Empire's failed attempts at Arctic exploration to the eruption. Oh, and did I mention the first depression ever in the fledgling United States? All of this is aside from the directly catastrophic events like the staggeringly enormous pyroclastic flow, the tsunami, and the devastating famine due to the loss of a growing season (or three).