The Lusitania Effect: America's Mobilization against Germany in World War I is the title of an article by Frank Trommler that appears on pages 241-266 of the May 2009 edition of German Studies Review. You can read the full text of the article at the link below.
Here is the article’s abstract:
The sinking of the Lusitania by a German submarine in 1915 became not only a crucial factor for the American entry into World War I, but unleashed an increasingly emotional drive of exclusion in the name of forging a new unity of the American nation. In the broader context the persecution of German Americans reinforced hysteria against socialists and other dissenters for the next half-century. A closer look at the battle for and against German culture reveals it as part of America's battle for its cultural independence, which became a fatal identity test for German Americans but also a challenge to American intellectual elites who maintained strong interest in German modernity and social policies.
Here is a general history of the Lusitania:
The RMS Lusitania was travelling from New York to Liverpool on May 7, 1915 carrying 1900 passengers. Both the British and American governments were aware of Germany’s declaration of unrestricted submarine attacks in British waters. Because of this, the British Admiralty had warned the captain of the Lusitania to exhibit caution and attempt to evade the German forces in the area. The captain did not heed these warnings and the Lusitania was hit by a torpedo and sank near the coast of Ireland.
At the time, the United States was remaining neutral in World War I. However, due to the sinking of the Lusitania, and the subsequent sinking many other American liners and other boats carrying Americans, the public opinion in America became decidedly anti-German. The United States officially entered the war on April 4, 1917. The sinking of the Lusitania is seen as the catalyst to the entrance of the United States into the war.