Final answer:
President Wilson's response to the Lusitania's sinking remained neutral at first, but increasingly hostile actions by Germany eventually led to the breakup of diplomatic relations and a war message to Congress.
Step-by-step explanation:
President Woodrow Wilson's response to the sinking of the Lusitania by a German U-boat in 1915 was measured and intended to maintain American neutrality. Despite the loss of 128 American lives, Wilson's initial reaction did not involve severing diplomatic ties with Germany or demanding reparations. It was not until the German Navy resumed unrestricted submarine warfare and the Zimmermann Telegram was intercepted, which proposed a German-Mexican alliance against the United States, that Wilson's stance hardened. In February 1917, after a series of aggressive submarine attacks on American merchant ships, Wilson broke off diplomatic relations with Germany. By April of that year, the situation escalated further, prompting President Wilson to deliver a war message to Congress, ultimately leading to a declaration of war on April 4, 1917.