Hello. Although you showed the book to which the question refers, you did not say which incident the question refers to, as there are many incidents covered in the book. This makes it impossible for your question to be answered, but I will try to help in the best possible way.
The main factor that points to the transition from old forms of war to new forms of war during the first world war was the use of technologies, mainly those driven by the industrial revolution, which gave the army a warlike power never seen before and allowed each army had access to fighter planes, tanks, submarines, toxic gases and others that did not exist in previous wars and that caused much greater destruction.
The middle of the sentence or after it states what's happing in the story your reading
