What event marked the beginning of an intense national alarm commonly referred to as the Red Scare?

The success of communists in Russia marked the beginning of an intense national alarm known as the Red Scare. Following the Bolshevik Revolution of 1917, the establishment of a communist government in Russia prompted fears of a similar uprising occurring in other countries, particularly in the United States. This ideological shift raised concerns among Americans about the potential spread of communism and the idea that radical leftist movements could destabilize society. As a result, various political, social, and economic reforms were enacted across the nation in an effort to suppress perceived threats and maintain social order.

The other events listed, such as the attack on Pearl Harbor and the assassination of Archduke Ferdinand, are significant moments in history but do not pertain to the fears surrounding communism. The signing of the Treaty of Versailles is related to the end of World War I and the geopolitical landscape of the time but does not directly connect to the American response to the rise of communism in Russia.