Complex sentence: These air raids killed around 670 people, injured 1,960 and caused great terror among London's population, though of far greater impact was the number of Londoners who were killed in combat: about 124,000 young men never returned from the war.
Split into simpler sentences: These air raids in total killed around 670 people, injured 1,960 and caused great terror among London's population. A far bigger impact was of the number of Londoners who were killed in combat; about 124,000 young men never returned from the war.