https://www.sciencedaily.com/releases/2021/11/211111130325.htm > Large eruptions create a cloud that blocks some sunlight for a year or two. That reduces warming of the land in Asia in the summer and leads to a weaker monsoon and less rainfall, reducing crop harvests. > "We confirmed for the first time that collapses of dynasties in China over the last 2,000 years are more likely in the years after volcanic eruptions," said co-author Alan Robock, a Distinguished Professor in the Department of Environmental Sciences in the School of Environmental and Biological Sciences at Rutgers University-New Brunswick. "But the relationship is complex because if there is ongoing warfare and conflict, dynasties are more susceptible to collapse. The impact of a cooled climate on crops can also make conflict more likely, further increasing the probability of collapse."