His family migrated to America while he was a child, with the assistance of the Hebrew Immigrant Aid Society. He went to school in Connecticut, graduating in 1910. Rather than study engineering at Yale University, the young Horwitz and a friend decided to launch a grocer's in Manhattan. As a member of the National Guard of the United States Horwitz was called into service under John J. Pershing to participate in the Pancho Villa Expedition. When he returned, he found the grocery business had been bankrupted. Horwitz then served in World War I in France as a sergeant, and as a cavalryman in Argonne.