There was stable & regional unity throughout the period of medieval Europe and Japan because of their society system.
What did medieval Europe and Japan have in common?
The Japanese and European societies were built on a system of hereditary classes, that is, the nobles were at the top, followed by warriors, with tenant farmers or serfs below.
However also, there was stable regional unity throughout the period of medieval Europe and Japan because of their society system.
Therefore, the Option B is correct.
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