The United States had been officially neutral in the war up to that point, but the sinking of the Lusitania led President Woodrow Wilson to issue a strong protest to the German government. In his note, Wilson warned that the United States would hold Germany accountable for the deaths of American citizens.
The German government responded by stating that the Lusitania had been carrying munitions and troops, making it a legitimate target. However, this claim was later disputed by the British government, and many Americans believed that the German U-boat had deliberately targeted a civilian vessel.
In the aftermath of the Lusitania sinking, the United States took several steps to increase its military preparedness and to put pressure on Germany. The Wilson administration expanded the size of the US Navy and began training a civilian reserve force. The US government also imposed restrictions on trade with Germany and its allies.
These measures failed to deter the German government, which continued to sink merchant ships and kill civilians. In April 1917, the United States declared war on Germany. The entry of the United States into the war proved to be a major turning point in the conflict, and the Allies eventually emerged victorious.
In summary, the sinking of RMS Lusitania angered the United States and contributed to its decision to enter World War I. The deaths of American citizens on board the Lusitania fueled public outrage and led President Woodrow Wilson to take action against Germany.