Complex sentence: Luigi Galleani (1861--November 4,1931) was an Italian anarchist active in the United States from 1901 to 1919, viewd by historians as an anarchist communist and an insurrectionary anarchist.
Split into simpler sentences: Luigi Galleani (1861--November 4,1931) was an Italian anarchist who was active in the United States from 1901 to 1919. Galleani is today viewed as an anarchist communist and an insurrectionary anarchist.