Final answer:
The U.S. government justified its World War I involvement through self-defense, spreading democracy, and economic expansion, which is 'All of the above' according to the given options.
Step-by-step explanation:
The U.S. government justified its involvement in World War I to the American public through a combination of factors. The Wilson administration sought to spread democracy across the globe, which wrapped U.S. participation in a principled cause. Additionally, the war presented economic opportunities through the expansion of trade and markets, thus potentially benefiting American economic expansion. However, in the face of aggressive actions of belligerents, such as the unrestricted submarine warfare by Germany, the idea of self-defense became a pertinent justification as well. The American First propaganda campaign pushed the notion that Americans needed to support the war effort to ensure national security and unity, despite some public resistance.
Thus, the U.S. government justified its involvement in World War I to the American public by emphasizing the need to protect the nation (self-defense), the principled mission to promulgate democracy, and the economic benefits that would come with victory, which in sum means 'All of the above' would be the appropriate option for the given multiple-choice answers.