The First Red Scare was a period during the early 20th-century history of the United States marked by a widespread fear of far-left extremism, including but not limited to Bolshevism and anarchism, due to real and imagined events; real events included the Russian 1917 October Revolution and anarchist bombings. At its height in 1919–1920, concerns over the effects of radical political agitation in American society and the alleged spread of communism and anarchism in the American labor movement fueled a general sense of concern.