Final answer:
The main idea of President Wilson's 1917 declaration is that the U.S. is formally declaring war on Germany, pledging to use all military forces and resources to end the conflict, due to Germany's aggressive acts, including unrestricted submarine warfare and provocations like the Zimmermann Telegram.
Step-by-step explanation:
The main idea of President Woodrow Wilson's declaration of April 6, 1917, is that due to the repeated hostile actions and acts of war committed by the Imperial German Government against the United States, Congress has resolved to formally declare a state of war between the two nations. The United States Congress authorized President Woodrow Wilson to employ all naval and military forces and pledged the country's full resources to carry on war against Germany and bring the conflict to a successful termination. The excerpt from Wilson's declaration conveys the United States's decision to enter World War I after maintaining a stance of neutrality due to factors such as the German unrestricted submarine warfare, the sinking of American ships, and the Zimmermann Telegram, which proposed a military alliance between Germany and Mexico against the United States.