Which of the following upset the United States and moved it closer to entering the war?

The Zimmermann Telegram proposed a German alliance with Mexico against the United States if America entered the war. When the telegram became public in 1917, it angered Americans and helped move the United States toward entering World War I. The British blockade and restrictions on U-boat warfare did not provoke the United States in the same direct way.

AI-written and checked against the verified answer.