Anglophiles and Francophiles supported the United States' entry into the war on the side of the Entente. German-Americans and Irish-Americans, meanwhile, supported the notion of the United States' entry into the war on the side of the Central Powers.

It's important to note that even up to the date of the American declaration of war, there was a wide range of opinions in regard to the proper American action. Should the United States remain neutral? Should it be neutral but friendly to the Entente? Should it be neutral but enforce its right to free trade with blockaded Germany and Austria? Should it enter the war, and if so, on whose side?

German-Americans favored either neutrality or entry onto the side of the Central Powers. They were joined by Irish-Americans who took a hard line against Great Britain, which they saw as occupying Ireland. Anglo-Americans, meanwhile, saw it only proper that the United States back Great Britain, which founded the American colonies.

The timing of the sinking of the Lusitania was particularly auspicious for the Entente, as it came just as America's free-trade dispute with Britain and France were reaching new heights. At the time, there was a vocal section of the American populace that insisted that the British and French blockade of Germany was illegal, and protested strongly to the British and French governments.

After the British and French governments announced their blockade, the Germans announced their counterblockade ─ conducted with submarines in waters around the British Isles. The sinking of the Lusitania followed in short order.