Final answer:
The U.S. declared war against Germany due to unrestricted submarine warfare, which included the sinking of American ships, and provocations like the Zimmermann Telegram, heightening tensions and challenging American neutrality.
Step-by-step explanation:
One of the reasons the U.S. declared war against Germany in World War I was due to Germany's policy of unrestricted submarine warfare. The sinking of American merchant ships like the Laconia and others by German U-boats violated the rights of America as a neutral nation and directly challenged the international principle of freedom of the seas. Germany's aggressive acts brought a strong public and political pressure on President Wilson, which led to his request to Congress to declare war and the subsequent U.S. entry into World War I.
Unrestricted submarine warfare was a key tonic, as it affected American economic interests and attacked the notion of freedom of the seas, a concept dear to the American psyche. The sinking of unarmed American freighters and the announcement of this policy by Germany escalated tensions, with the goal of disrupting British trade routes. Additional provocations, like the infamous Zimmermann Telegram, in which Germany attempted to entice Mexico into an alliance against the United States, galvanized the American decision for war, as this threatened American sovereignty and territory. These acts, compounded with the use of propaganda highlighting the moral struggle and the democratic ideals of the conflict, helped shape the narrative for American involvement.