Unrestricted submarine warfare was first introduced in World War I in early 1915 when Germany declared the area around the British Isles a war zone, in which all merchant ships, including those from neutral countries, would be attacked by the German navy. A string of attacks on merchant ships followed, culminating in the sinking of the British ship Lusitania by a German U-boat on May 7, 1915. Although the Lusitania was a British ship and it was carrying a supply of munitions—Germany used these two facts to justify the attack—it was principally a passenger ship, and the 1,201 people who drowned in its sinking included 128 Americans. The incident prompted U.S. President Woodrow Wilson to send a strongly worded note to the German government demanding an end to German attacks against unarmed merchant ships. By September 1915, the German government had imposed such strict constraints on the operation of the nation’s submarines that the German navy was persuaded to suspend U-boat warfare altogether.
The Second World War earned the United States a place at the grown ups table because they showed the rest of the world they were not to be trifled with. Both with their troops fighting and the fact that they were able to finish making the atomic bomb before an old, well established country like Russia.