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. rephrase as a 9th grader shorten

National identity is a recent concept that developed due to four key changes in our modern society: urbanization, the necessity for a shared language, advancements in technology such as newspapers and trains, and the significant impact of warfare.