In American history

History of the United States (1918–1945)

The history of the United States from 1918 through 1945 covers the post-World War I era, the Great Depression, and World War II. After World War I, the U.S. rejected the Versailles Treaty and did not join the League of Nations....

, the First Red Scare of 1919–1920 was marked by a widespread fear of Bolshevism

Bolshevik

The Bolsheviks, originally also Bolshevists , derived from bol'shinstvo, "majority") were a faction of the Marxist Russian Social Democratic Labour Party which split apart from the Menshevik faction at the Second Party Congress in 1903....

 and anarchism

Anarchism

Anarchism is generally defined as the political philosophy which holds the state to be undesirable, unnecessary, and harmful, or alternatively as opposing authority in the conduct of human relations...

. Concerns over the effects of radical political agitation in American society and alleged spread in the American labor movement fueled the paranoia that defined the period.

The First Red Scare had its origins in the hyper-nationalism of World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. At the war's end, following the Bolshevik revolution in Russia

October Revolution

The October Revolution , also known as the Great October Socialist Revolution , Red October, the October Uprising or the Bolshevik Revolution, was a political revolution and a part of the Russian Revolution of 1917...

, American authorities saw the threat of revolution in the actions of organized labor, including such disparate cases as the Seattle General Strike and the Boston Police Strike

Boston Police Strike

In the Boston Police Strike, the Boston police rank and file went out on strike on September 9, 1919 in order to achieve recognition for their trade union and improvements in wages and working conditions...

 and then in the bomb campaign

1919 United States anarchist bombings

The 1919 United States anarchist bombings were a series of bombings and attempted bombings carried out by anarchist followers of Luigi Galleani from April through June 1919...

 directed by anarchist groups at political and business leaders.