Which nation has had the most influence over the development of
Japan? *

*The previous answer from the other person is plagiarized just a warning*

China

Explanation:

After Japan develops into a more complex Kingdom, their neighbours were China, whom was ahead of its time in politics, culture, technology and philosophy. Though the greatest influence was from Prince Shotoku Taishi, he loved the Chinese system, even sending diplomats to study there in order to learn more. This greatly influenced the Empress at the time (Empress Suiko) which overall impacted Japan even more. Therefore the nation that influenced Japan's development the most is China.

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the fact that could also be added to column b is that during world war ii, specifically between the years 1941 and 1945, japan expanded its territory towards the indonesian territory in what was known later as part of the "pacific war". in that time, japan could conquer the philipines, singapore,   borneo, central java, malang, cebu, sumatra and various other islands of the area, therefore expanding its territory for a brief period of time.