Otto and Robert Frank (back center) with their cousins Oscar (back left) and George (back right), Helene Frank (center left) and Jean-Michael (front).On 3 August 1914 Germany declared war on France. Apart from Jean-Michel, who was still a minor, all the sons in the Frank family went to fight in the war. While Otto and his brothers fought for Germany, their cousins from Paris fought on the French side.