Final answer:
Germany announced it would begin unrestricted submarine warfare during World War I on February 1, 1917, to cut off supplies to the Allies from the US, a decision that played a role in bringing the United States into the war.
Step-by-step explanation:
During the years leading up to World War II, Germany announced a series of aggressive policy decisions as part of its strategic military planning. After having withdrawn from the League of Nations in 1933, Germany began re-arming secretly by 1935, which was a direct defiance of the Treaty of Versailles. This militaristic buildup was later followed by the occupation of the Rhineland, the annexation of Austria, and the occupation of the Sudetenland as agreed upon at the Munich Conference.
However, the question seems to refer more specifically to World War I, as it mentions the decision to commence unrestricted submarine warfare on February 1, 1917, an action that was calculated by the German Empire in the hope that it could cut off the supplies to Britain and France being shipped from the United States, speeding up a potential victory. This new policy led to the sinking of American ships and played a significant role in the eventual involvement of the United States in WWI after the release and anger caused by the Zimmermann Telegram. Ultimately, these actions by Germany were part of their larger strategy to shift the tides of war in their favor and are an illustrative example of how military decisions can have wide-reaching geopolitical consequences.