How did the heian period start

Kyoto or Heian period began when the capital of Japan was shifted.

Explanation:

The historical capital of Japan in the 8th century befell a number of natural disasters and the kingdom was plagued by the destruction wrought by the disasters.

The emperor Kanmu decided to move the capital to the new site which was the city of Heian kyo , which is not known as Kyoto.

This brought a period f stability of 400  years when Japanese art influenced b a variety of sources reached its artistic and cultural peak.  The period was also when the kingdom was  not attacked and unchallenged from within.

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the answer is b, encourage free trade