*The previous answer from the other person is plagiarized just a warning*
Answer:
China
Step-by-step 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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