why, despite its limited charge and the many other atrocious acts committed during the war, was Nanking made the emblematic event of the Pacific War?

I’m looking for help with my research proposal– mainly explaining the significance of a question (which I included, but am open to changing if it remains in the general area of Nanking China) and what the goals and objectives are, as well as some background on the topic. I’ve included a rough outline, and if possible, please stick to the ratio of page limits for each section.