Complex sentence: Among the more notorious of the anarchists deported under the act were Luigi Galleani and several of his adherents; the "Galleanists" were responsible for a deadly bombing campaign that had reached new heights in 1919 and 1920.
Split into simpler sentences: Among the more notorious of the anarchists deported under the act were Luigi Galleani and several of his adherents. They had been responsible for a deadly bombing campaign that had climaxed in 1919 and 1920.