Complex sentence: In February, 1915, the U.S. sharply warned Germany about misuse of submarines but on May 7, the British passenger liner "Lusitania" was torpedoed with the loss of 1,198 civilians, including 128 Americans.
Split into simpler sentences: In February, 1915, the U.S. warned Germany about misuse of submarines. On May 7, Germany torpedoed the British passenger liner "RMS Lusitania", resulting in the loss of 1,198 civilians, including 128 Americans.