by the middle of the nineteenth century, what factors
threatened the isolation and stability of japan?

Japan had a strict policy of isolation and was not interested in trading with any nation especially from the West. They knew the advancements that were made since they had a little contact with the Dutch. And then in 1853 U.S. Commodore Matthew Perry and his fleet forced Japan to open up and end its isolation. This was followed by a brief civil war and then with a rapid industrialization of Japan.

answer; the period of time known as the middle ages;

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