The 1923 Great Kanto earthquake

Every now and then, there is some evidence for the moral progress of mankind.  Looking back in time, Wikipedia reports:

One particularly pernicious rumor was that Koreans were taking advantage of the disaster, committing arson and robbery, and were in possession of bombs. In the aftermath of the quake, mass murder of Koreans by brutal mobs occurred in urban Tokyo and Yokohama, fueled by rumors of rebellion and sabotage. About 6,600 Koreans were murdered. Some newspapers reported the rumors as fact, which led to the most deadly rumor of all: that the Koreans were poisoning wells. The numerous fires and cloudy well water, a little-known effect of a large quake, all seemed to confirm the rumors of the panic-stricken survivors who were living amidst the rubble. Vigilante groups set up roadblocks in cities, towns and villages across the region. Because people with Korean accents pronounced “G” or “J” in the beginning of words differently, 円 銭 (jū-go-en, go-jū-sen) and がぎぐげご (gagigugego) were used as a shibboleth. Anyone who failed to pronounce them properly was deemed Korean. Some were told to leave, but many were beaten or killed. Moreover, anyone mistakenly identified as Korean, such as Chinese, Okinawans, and Japanese speakers of some regional dialects, suffered the same fate. About 700 Chinese, mostly from Wenzhou were killed.

On modern-day Japan, Edward Hugh has an excellent post.