Question

How did the sinking of the Lusitania in 1915 affect World War I?

Answer 1

The sinking of the Lusitania brought the U.S into WW1,

As it was a passenger ship so the U.S had rights to attack Germany, while Germany protested that it was transferring weapons to the Entente (which it was). The U.S joining the war helped the Entente beat back the Central Powers majorly, or became one-sided if that helps.

Answer 2

 America was shipping war material to England and France. Germany declared unrestricted submarine warfare, warning that any and all ships