Between 1630 and 1853, Japan experienced a period of self-imposed isolation from outsiders. What geographical feature most influenced Japan's isolation?

Japan is an island state, the sea plays a huge role in the development of this country. The sea as a geographical characteristic most influenced the isolation of Japan. The emergence of Europeans in the Japanese islands not only contributed to the aggravation of internecine wars feudal lords, gave impetus to the development of maritime trade, but also caused the risk of subordination of Japan to European colonizers, because the Spaniards and Portuguese took Participation in internecine wars on the side of the Southern feudal lords. In the reality of the European threat, the Japanese could see the example of the Philippines captured by the Spaniards.