Cause: a new variant strain of the bacterium Yersinia pestis.
The third plague pandemic as it became known began in that began in Yunnan, China, in 1855 and spread to all inhabited continents. It led to more than 12 million deaths in India and China alone. According to the World Health Organization, the pandemic was considered active until 1960, when worldwide casualties dropped to 200 per year. Deaths have continued at a lower level every year since.
Killed >15 million with the majority in India and China