I think its safe to say, no Christian group has been so hounded, persecuted, and slaughtered, BY OTHER CHRISTIANS, as have French Calvinist Protestants (Huguenots). Mostly over 400 years ago...but still.
Very sad story indeed.
You might want to look into the Waldensians.
After France's King Louis XIV issued the Edict of Fontainebleau in 1685, which revoked the Huguenots' right to practice their religion, many fled to Prussia, a rising power whose growing army welcomed young Huguenot men, some of whom would rise to positions of leadership and join the Prussian military elite. Prussia's gain was France's loss. In WWI, German General Hermann von François, who was descended from Huguenots, would torment France's ally Russia and fight the French at Verdun.