In 1290 Edward I expelled the Jews from England. No reason has been recorded.
It was often people part of the IRA or UVF during the troubles
Kurds.
Japanese Americans
christians
During World War II the Nazis persecuted and killed millions of Jews, Polish, Slavic and Romani people, the mentally and physically disabled, the deaf and blind, homosexuals, and political adversaries like communists, socialists, and social democrats.
It was the Tutsis that were being persecuted, by the Hutus.
Judaism was persecuted by the Soviet Union. Jews have been persecuted almost constantly.
Stallingrad
The Sinti and the Roma were lumped together under the heading "Gypsies", and, like almost every other group that weren't pure Aryan, they were persecuted and murdered as "undesirables" by the Third Reich.
Jews were not the only people who suffered. But, along with the Gypsies they were the only people who were persecuted for their heritage, rather than choices that they made.
People are sometimes persecuted for belonging to a certain ethnic group (jews are not only a religion but also an ethnic group; also negroes, other non-whites in many countries), other minorities or majorities (e.g., homosexuals, women, etc.). Basically, anybody who is "different" from what a group in power considers the norm.
Quakers