The organized destruction of an ethnic group is called a pogrom. The word comes to English via the similar Yiddish and Russian words; pogrom literally means "devastation."
In many Russian pogroms in the late 1800s and early 1900s, the mob attacked Jews — burning their homes and synagogues. Thousands of Jews were killed during these attacks, and many more fled them by emigrating to other countries, including the United States. Pogroms against Jews occurred in countries other than Russia, including Argentina, Romania, Poland, and Libya. Other ethnic groups, including Armenians, were also the target of pogroms in the early twentieth century.