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Unrestricted submarine warfare, a tactic employed by Germany during World War I, involved attacking enemy shipping without warning. This strategy was a significant factor in the United States' decision to enter the war.123

Initially, Germany restricted its submarine warfare due to concerns about provoking the U.S. However, by February 1917, the German naval command, supported by military leaders, decided to resume unrestricted submarine warfare, believing it was crucial to overcome the British naval blockade and starve Britain into submission.14

The sinking of the British ocean liner Lusitania in 1915, which resulted in the deaths of 128 American citizens, was a major incident that fueled anti-German sentiment in the U.S. and contributed to the eventual declaration of war. Despite the effectiveness of submarines in sinking Allied and neutral ships, the introduction of the convoy system, along with improved anti-submarine technology and increased shipbuilding, ultimately countered the German U-boat campaign.324

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