The concept of national identity is relatively new, emerging as a result of four significant changes during the modern era: urbanization, the need for a common language, advancements in technology (such as newspapers and trains), and the transformation of war into a large-scale, all-consuming phenomenon. rephrase as a 9th grader shorten

National identity is a new idea that came about because of four important changes in modern times: people moving to cities, the need for a common language, improvements in technology like newspapers and trains, and war becoming a big deal.